Chase Bodor, Author at Plastics Plus Technology, Inc.

Design for molding is a niche discipline that challenges even the best engineers. There are many considerations that affect the final composition of your part. These design decisions can lead to manufacturing inefficiencies, costly defects, and delays. But, when a designer takes the time to evaluate their design and mitigate risks, there is opportunity for success.

If you want to design production ready parts – this is the guide to get you there.

Plastic Part Design Process:

Step 1: Define End-Use Requirements

The first step in the product development phase is completing a thorough assessment of the product specifications and end-use requirements. A complete product design specification helps other engineers down the value stream understand the required critical design features. This information should also be quantitative rather than qualitative when possible because this data allows for more informed decisions in the design process. Furthermore, quantitative information, rather than qualitative, allows for better informed design decisions.

However, this can be tricky for prototypes due to the lack of part history. If there is no previous data to inform your design decisions, then a prototype may help inform some of those requirements. As the design matures, use the new data as inputs for the final production part.

Step 2: Create a Preliminary Concept Model

Creating a preliminary model will help your engineering team identify the critical tolerances and design features of the part. This also helps your manufacturing partner understand the features that are critical to quality. If the manufacturer knows what is/ is not critical to quality, they will produce better parts with competitive prices. Your manufacturing partner can also help you optimize part features to simplify tooling.

Step 3: Material Screening

There is an overwhelming array of thermoplastic resin compounds available to you. How do you decide which material best suits your needs? First you want to scout materials with properties that match your end-use requirements. One way to research material properties is to use a resin database like UL Prospector or MatLabs. Start by eliminating the resin families that do not have the material properties you’re looking for such as chemical resistance, thermal properties, or appearance qualities. Once you’ve made your shortlist, compare these material properties side by side. Give yourself enough options so you have flexibility later on.

Step 4: Design Part Around Materials

Now that you have a few materials selected it is time to design your part. But remember, each material has different properties that can affect the geometry of the part. For example, designing with nylon versus a polypropylene would result in thinner wall sections with nylon due to its flow and rigidity properties. Similarly, an HDPE resin would require you to design the part with thicker wall sections which may cause some issues in an assembly where the fit is critical. These are all important factors that make the design process more challenging and cumbersome.

Step 5: Final Material Selection

Once you have compared the design characteristics for each of the selected materials, it’s time to select the one that best matches your needs. Think about this from a few different perspectives: cost, performance, processability, and availability. You want to choose the one that fits the end-use performance criteria. But you also may want to consider how easily that material processes because that can have an effect on the overall manufacturing costs of the product. Hard to process material also results in higher defect rates which triggers higher inspection levels and potentially more scrap. Ultimately, choosing the best material that fits your needs, budgetary and overall performance in both processing and end-use is a key component in successful design projects.

Injection Molding Design Rules

Wall Thickness

Wall thickness is a critical design function for injection molding. This affects how the mold fills as well as the appearance and strength of the molded part. There are three key points to consider:

Uniform wall thickness
Nominal wall thickness
Recommended wall thickness

Uniform Wall Thickness

Uniform wall thickness allows the part to cool evenly and avoid costly defects. When a part consists of varying wall thicknesses it cools and shrinks at different rates. This causes defects such as shrink, warp, and others that affect the strength and appearance of the part. While some designers are okay with these defects in non cosmetic areas, they can cause headaches during inspection if the criteria are not clearly defined. Overall it is best practice to keep a consistent and uniform wall thickness whenever possible.

Nominal Wall Thickness

When a completely uniform wall thickness cannot be achieved, a nominal wall thickness is acceptable. Nominal wall thickness describes the thickness throughout the entire part. This means there are features that are thicker or thinner than the average wall thickness of the part. Be careful, thick and thin walls can affect the molding process negatively and cause quality problems. Let’s define what thick and thin walls are.

Thin Walls: Parts with less than 0.08” of wall thickness are considered thin walls. There are specialized molding techniques that allow you to mold these parts. However, these parts are typically uniformly thin. In non uniform design, thin walls tend to trap air and gas which prevents the plastic from filling the mold cavity completely. This results in short shots – where the molded part is not fully formed. These are typically rejected parts and are thrown away.

Thick Walls: Walls thicker than 0.16” (or thicker than the material recommends) can cause problems too. First, thick walls increase the overall cycle time for each shot. This can impact the cost of each part even if the cycle is just a few seconds longer. Furthermore, thick walls will cool slower than thin walls which causes warp, sink, and voids.

Recommended Wall Thickness

Each resin has a recommended wall thickness specified in its material profile. Whenever you are designing a new part you should refer to these values and adjust your part’s wall thickness appropriately. Below is a quick reference table:

Recommended Wall Thickness by Resin

Resin	in
Acetal	0.030 – 0.120
Acrylic	0.025 – 0.15
ABS	0.045 – 0.14
Nylon	0.030 – 0.115
PBT	0.080 – 0.250
PC	0.040 – 0.150
PEEK	0.020 – 0.200
PEI	0.080 – 0.120
PE	0.030 – 0.200
PPSU	0.030 – 0.250
PP	0.040 – 0.15
PS	0.025 – 0.125
TPE	0.025 – 0.125
TPU	0.025-0.125

These values are derived from publicly available information. Optimal wall thicknesses can vary depending on the geometry of the part. We recommend reviewing your design with a plastics engineer to optimize the wall thickness throughout the part.

Transitions

If your part requires different wall thicknesses, then the transition from thick to thin needs to be blended smoothly. Sharp steps and corners between different wall thicknesses will hinder the flow of material and compromise the part’s integrity. The best way to avoid this is by using fillets and chamfers to round out the transitions.

Fillets – rounded corners or edges
Chamfers – 45deg angled edges connecting two surfaces.

Corners

Where possible, corners should be rounded with proper radii. Rounded corners reduce stress concentrations in the part, which can cause defects that create aesthetic or functional problems. They also minimize plastic shrinkage so that corners are even. Calculating the radius on a rounded corner is simple:

Internal radius 50% of wall thickness (assuming nominal thickness)
For the external radius, use your wall thickness measurement and add the internal radius value (R2=R1 +Wt)
Both internal and external radii need to originate from the same point.
Parts with equal internal and external radii will end up with a corner that is either too thick or too thin.
Sharp corners often require EDM machining, a process that is precise but costly.

Ultimately, using rounded corners not only promotes better moldability, they also simplify the moldmaking process making your part easier to manufacture and buy at a reasonable cost.

Draft

Applying the right amount of draft is a crucial part of the design process for injection molding. Draft is an angle applied to vertical walls that allow the part to eject from the mold. Essentially, the draft allows for the steel to clear away from the molded part without damaging it. A good rule of thumb is to use 1 degree of draft per side for every 4 inches of length. Be sure to consider the pull direction, how the mold separates, to determine the draft direction.

A quick note: draft angle specifications vary from material to material and can be influenced by the texture of the mold. To find out how much draft you need to apply, we suggest using the Society of Plastics Industry (PLASTICS) standards and Mold-Tech for guidance.

Ribs:

Sometimes, an engineer will design a part with thin walls; reducing material usage, speeding up production, and promoting longer tool life. However, these thin walls lack the load-bearing capacity and do not have the structural strength required for the application on their own. Ribs are a design feature that add strength and support to thin walled parts. Using a vertical rib gives these walls additional strength and can even reduce warp with certain geometries.

Like many injection molding design features, ribs require a bit of homework to design properly. Thick ribs have a tendency to produce sink marks, and thin ribs do not provide enough strength and may potentially end up not fully filled.

Here are some more design rules for ribs:

Wall thickness: should be 50-60% of nominal wall thickness
Fillets: should be used at the base of ribs to avoid sharp transitions. An appropriate radius is 25-50% of the nominal wall thickness, but should be no greater than 0.01”
Height: Keep rib heights to a minimum, no more than 2.5X the wall thickness. If you need more support for taller walls then add ribs no less than 2X the wall thickness from each other.
Draft: Apply at least 0.5 degrees per side.

Bosses:

Bosses are another popular design feature used in injection molding. These vertical features are used in assembly applications to receive fasteners such as screws, pins, or even smaller bosses. Like ribs, bosses also increase the structural strength of a part when designed appropriately.

Here are a few golden rules to follow when designing bosses:

Size: the inner diameter of a boss is likely to shrink as the part cools. It is essential that you reference the material’s shrink properties when adding a boss and design the feature accordingly. The overall size of the boss should be between 2-2.5X the size of the inner diameter of the part.
Thickness: Like many other plastic features, thickness matters. Bosses that are too thick are prone to sink, which can be an eyesore. We recommend that bosses are no more than 60% of the overall wall thickness.
Location: Place boxes where structural integrity is needed such as screw holes.
Walls: Alignment when attaching bosses is key. These bosses need to align with other features of the part or mating part to prevent assembly mismatch. Also, avoid thick wall sections when attaching a boss to a wall. One option is to core out sections of the thick area to make a uniform wall section.

Parting Lines:

A parting line refers to the line created at the point where the two halves of the mold meet when closed. Depending on the aesthetic requirements and geometry of the part, the parting line can be moved around to fit your needs. There are a few places where parting lines can be placed to help simplify the mold construction, such as sharp corners. And there are some places where parting lines should not be placed such as on filleted surfaces. Finally, it is important to note some of the common defects that happen at the parting line which is an indication of the overall health of the mold. Defects such as parting line flash, mismatch, and stress marks are indications that either some tool work needs to be done or that the mold was not installed properly.

Gates:

A gate refers to an opening in the injection mold where molten plastic enters and fills the cavity. There are many types of gates in injection molding. Some gates enable better material flow through the cavity which allows the mold to fill fast and complete. While others offer better appearance results or eliminate extra manufacturing steps. This all depends on the part geometry and features.

Before we dive into the different types of gates we need to discuss two critical decisions: location and size.

Gate Size: The size of the gate is important because it controls the flow volume of the material into the mold. Larger parts, and materials with a low melt flow rate (MVR), need larger gates. If the gate is undersized, the part is at risk of not fully forming. However, oversized gates are harder to trim and waste material. Thankfully, thermoplastic materials come with a gate sizing specification which can be used to calculate the proper size for the gate.

Gate location: The gate location has a huge impact on the final part quality. For instance, the location determines the direction of material flows, where weld lines appear, and what features are the last to fill. This can result in defects such as short shots, voids, warping and others that can occur. To avoid potential defects, we offer mold flow analysis and a comprehensive mold design review.

Here are the different types available:

Edge
Fan
Tab
Sprue
Diaphragm
Ring
Spoke
Hot tips
Sub
Pin

Ejection

Ejection in injection molding is the process of removing the molded part from the mold cavity. This is one of the critical phases in the injection molding cycle, so ensuring your part can eject from the mold without any issues is crucial. In order to do this, we need to consider ejection throughout the design process. There are several key factors that affect the parts ability to eject, and of course, some golden rules too.

Let’s look at a few of these factors:

Draft Angles: Draft angles reduce friction during ejection, making it easier for the part to release smoothly from the mold. Deep parts require steeper drafts
Ejector Pins and Contact Points: Place ejector pins on flat, sturdy areas of the part to avoid visible marks and damage. Avoid positioning pins near delicate features, thin walls, or unsupported edges, as these can break or deform during ejection.
Wall Thickness and Reinforcement: Thin or sharp-edged features are prone to breakage. To improve ejection, maintain consistent wall thickness and add ribs or fillets to reinforce critical areas. Avoid thin walls near ejector pins, as they may deform or tear.
Textured Surfaces: For textured or rough surfaces, increase draft angles to prevent sticking and ensure a clean release.
Undercuts and Core Pulls: Avoid undercuts where possible, as they complicate ejection and may require additional mechanisms like core pulls. Designs with minimal undercuts allow for simpler, more reliable ejection.

The information provided in this guide is public information and should be used as a suggestion for part design. Specifications with more stringent requirements may require further investigation. Contact us for help and we can do a comprehensive DFM review with you and your team.

An injection molded part specification tells your molder exactly what the final product requirements are. Specifications are intended to inform engineers and satisfy the end-use requirements for the application. These requirements should include aesthetic, functional, environmental, and economic requirements. Therefore, the final part should match the complete set of molded part specifications.

These specifications should include:

Material (brand name, grade, generic)
Surface finish
Parting line location
Flash limitations
Gate location and weld lines (away from critical stress points)
Locations where voids are not allowed
Allowable warpage
Color (Pantone PMS)
Decorating requirements and artwork
Performance requirements and testing methods (if applicable)

If you’re submitting a request for quote for a new part – download this Design Form to ensure all of your specifications are documented and communicated.

Surface finish is a critical aspect of many plastic parts, as it can affect the part’s performance and aesthetic appeal. To ensure that the surface finish of a plastic part meets specifications, it is important to use proper measurement techniques that are accurate and repeatable. In this post, we will discuss the use of Geometric Dimensioning and Tolerancing (GD&T) principles and profilometers for measuring surface finish on a plastic part.

What is Surface Finish?

Surface finish refers to the roughness, waviness, and lay of a surface. In other words, it is characterized by the micro-geometry of the surface, including the size, spacing, and distribution of surface features. These features can include surface roughness, such as peaks and valleys, and surface waviness, which refers to the undulations in the surface.

Why is Surface Finish Important?

Surface finish is important for a variety of reasons. For example, it can affect the performance of a part by influencing factors such as friction, wear, and corrosion resistance. Additionally, a smooth surface finish can improve the aesthetic appeal of a part and increase its marketability.

How is Surface Finish Measured?

There are several methods for measuring surface finish, including visual inspection, tactile inspection, and instrumentation-based measurements. The most commonly used instrument for measuring surface finish is a profilometer. Profilometers use a stylus to scan the surface of the part and measure the variations in surface height. Then, the data collected by the profilometer is processed to calculate the roughness parameters of the surface, including roughness average (Ra), root mean square roughness (Rq), and more.

Using GD&T Principles for Surface Finish Measurement

In order to ensure that the surface finish of a plastic part meets specifications, it is important to use a consistent and repeatable measurement method. This is where GD&T principles come into play. GD&T is a system of symbols and rules used to define the size, shape, orientation, and location of a part. With GD&T symbols and rules, designers can specify the surface finish requirements of a part, including the maximum and minimum allowable roughness parameters.

For example, the GD&T symbol for surface finish is a wavy line that is placed adjacent to a feature of size. The wavy line represents the surface roughness and the number next to it represents the maximum allowable roughness in microinches (µin). By specifying the surface finish in GD&T, designers can ensure that the part is manufactured to the correct specifications and that the surface finish is accurately measured.

Conclusion

Measuring surface finish on a plastic part is an important step in ensuring that the part meets performance and aesthetic specifications. By using GD&T principles and profilometers, designers can specify the surface finish requirements of a part and ensure that the measurement is accurate and repeatable. By using these techniques, manufacturers can produce high-quality plastic parts that meet the needs of their customers.

For more information on how we can help you achieve a desired surface finish, please reach out to our engineering department at the number on our contact page.

The validation process is like a charcuterie board of overhead costs… And if your quality requirements are stringent – you’re going to need an appetite.

When looking at the overall cost of an injection molding project, it’s easy to quantify and even justify the costs of upfront tooling. Same with the price per unit of each part. But when we start talking about validation processes, things are not always as clear. Therefore, costs can easily begin to compound when the process is not monitored and carried out properly.

First, you want to have the right people.

Validating new products and components requires oversight from Quality and Engineering SMEs. These experts are no slouches – often leveraging specialized skills in processing, measuring, data analysis, and other high-value skills. Their time and knowledge are worth their weight as long as the processes and systems they have to follow can make the best use of them.

That’s where having the system to test, record, assess, and the document becomes so valuable.

It will help you plan, check, and monitor your expenses throughout the validation process. This allows you to make quicker, more informed decisions to stay on budget.

If not, then validation overhead could end up being a significant (or even the biggest) cost driver. You don’t want this process to eat up all your budget.

💡 Here are 8 ways you can keep your validation overhead controlled:

🔎 Utilizing industry standards and guidelines for validation, such as ISO 13485 and ISO 9001, to ensure that all necessary validation processes are being followed.

🚨 Implementing a risk management process to prioritize and focus validation efforts on the most critical aspects of the device.

🚌 Streamlining validation protocols and procedures to minimize duplication of effort and increase efficiency.

💻 Automating validation testing and record-keeping, using electronic systems to reduce manual errors and increase accuracy.

🔎 Continuously evaluating and improving validation processes to ensure that they are current and effective.

🤩 Outsourcing validation services to third-party providers, which can provide specialized expertise and resources.

🔧 Using a modular approach in design, where different parts of the device are validated separately, which can reduce the overall validation effort.

📄 Utilizing device history records, which can provide a detailed record of the device’s history, which can be used to demonstrate compliance with regulatory requirements.

If you struggle to accurately control your validation processes and you’d like to chat about how to improve your process – reach out to us! Plastics Plus Technology operates a QMS that strictly follows ISO 9001:2015 and ISO 13485:2016 requirements.

The mold build designed to shorten time-to-market and reduce tooling costs.

Have you ever approached an injection molder looking to source a quote for a project still in the development phase? If so, you might have balked at the initial tooling price. Why on Earth would you invest so much upfront on a project you’re not sure will succeed on the market?

Well, there’s another tooling option that you might not be aware of – MUD units. In a nutshell, a MUD unit is capable of making quality, precision parts without the price tag. This is the perfect tool build to produce a short run for your engineering or market tests.

In this article, we’ll go into more detail about what a MUD unit is and how it works. You’ll also find the benefits of this type of build and its capabilities. Finally, we’ll send you home with some notes to take back to your engineering team. If you have further questions, please reach out!

What is a MUD Mold Base?

A MUD – or Master Unit Die – is a modular mold base that houses interchangeable cavity and core inserts. These builds use a standard-size mold frame that can be left in an injection molding machine while a mold technician completes a changeover. In other words, the molder can change molds by simply removing the core and cavity inserts and replacing them with another compatible set. This is ideal when you have multiple product configurations or a product still in development.

What Does a MUD Base Do?

MUD bases are a cost-effective, yet productive alternative to full-sized molds (full chase). The modular nature of a MUD unit allows molders to quickly switch mold configurations or even to other products with minimal downtime. Once the mold frame is in place, the molder can quickly change out the core and cavity inserts in favor of a different set. In just a few steps, the manufacturer can go from molding one product to another.

Choosing a mold base will still allow you to build *thousands of parts with quality and precision. In fact, the ability of these tools is on par with small and medium-run injection molding tools. Furthermore, many mold builders can build these while incorporating hot runners and other mold accessories to drive better manufacturing results.

MUD Bases and Project Development

It is true – MUD bases are perfect for projects that are still in development or going through design changes.

Having removable inserts makes troubleshooting and making tooling adjustments much easier. This is mainly due to the technician not having to remove an entire mold base. In addition, the mold builder can work quicker by not having to disassemble multiple mold plates.

These inserts are typically made of P20 or H13 steel. The former is softer and therefore easier to machine. This makes modifying the tool to address a design change much more feasible. However, drastic changes to a design may require building new inserts completely.

Ultimately, this is better than having to build an entirely new mold.

Benefits of MUD Bases

We’ve covered a few of the benefits of MUD bases already. Here is a summary of those benefits:

· Setup time reduced from hours to minutes

· Quick/ easy to modify without removing an entire mold frame

· Minimal production downtime

· Easy to handle, use, install, and maintain

· Lower tooling build cost as you only need to purchase in A& B inserts and not the entire mold base.

· Lower molding processing costs from quick mold change reducing downtime

· Lower labor costs by reducing the number of techs working on one mold.

· Speed to market is improved by reducing machining time and workload.

· Sustainability – the frame can be reused with other inserts.

· Supply chain flexibility to support just-in-time scheduling

Types of MUD Bases and Frames

As we discussed, the core and cavity inserts have a ton of customization options. Mold frames on the other hand do not.

Mold frames are more standardized in size and build. For the inserts to have a proper fit and truly be modular– you need the proper frame shape. Fortunately, there are a handful of shapes available that allow you to be more flexible with your insert configurations.

Here are a few of the main ones:

U-frame: standard single insert

H-frame: standard double insert

Double H-frame: Standard 4 insert

E-Frame: side by side double insert

What You Do and Don’t Need to Know (Conclusion)

It is unlikely that you will have to decide for yourself which mold frame to go with. Your injection molder will have the insight to use the best frame for your MUD unit.

On the other hand, it is up to you to understand the capabilities and limitations of the MUD unit. While it is possible to have a MUD unit produce hundreds of thousands of parts – that is beyond its life expectancy. Furthermore, you should expect to see wear on the tool where there are moving parts (slides, cores, pins, etc.). This can cause issues with production and impact the final part quality or result in unplanned downtime.

Therefore, you should have a conversation with your molding partner to see if building a high-volume production tool is right for your project. At that point, you can plan an appropriate timeline for ramping up production and minimizing potential downtime.

Launching a new product soon?

If you’re planning to launch a project in the next year and need a MUD unit for market testing – we can get one built for you! Visit our website and fill out an RFQ form to start the process. We look forward to working with you!

Typical Steel Properties For Injection Molding Tools

Properties	Carbon steel	Alloy steel	Stainless steels	Tool steels
Density (kg/m3)	7850	7850	7750 – 8100	7720 – 8000
Elastic Modulus (GPa)	190-210	190 -210	190 – 210	190 – 210
Melting Point (oC)	1425 – 1540	1415 – 1432	1371-1510	1400 -1425
Tensile Strength (MPa)	276 – 1882	756 – 1882	515 – 827	640 – 2000
Hardness (Brinell 3000kg)	86 – 388	149 – 627	137 – 595	210 – 620
Yield Strength (MPa)	186 – 758	366 – 1793	207 – 552	380 – 440
Thermal Expansion (10^-6/ K)	11 – 16.6	9.0 – 15	9.0 20.7	9.4 – 15.1
Thermal Conductivity (W/m.K)	24.3 – 65.2	26 – 48.6	11.2 – 36.7	19.9 – 48.3

This chart for typical steel properties for injection mold tools is to be used for reference only and is public information. Plastics Plus Technology Inc and its partners are not responsible for decisions made based on this information alone.

Click here to view it in PDF format.

I recently stumbled upon “The Iceberg Problem”

It is well-known to software developers, but it isn’t unique to just them.

Manufacturers have an iceberg problem too.

This idea originates from the process of building custom products or services for customers. With any custom project, there is a chance for misaligned discourse between what the customer thinks they want and what the contractor perceives the customer’s needs are. This can be frustrating and even painstakingly miserable for both parties.

The common cause – most times customers don’t understand the complete process.

Like an iceberg – 90% of manufacturing happens beneath the surface. The other 10% is what the customer perceives to be the result of the work being done.

When you present the work to the customer:

They care about the looks – does it match their vision?
They care about the performance – does it works as intended?
They care about how much it costs them – did the budget align with their expectations?
They care when they will receive their order – does it match their timeline?

And that’s it. That’s the 10%.

How can that be? From what I have gathered, there are a couple of hang-ups that drive a wedge between the customer and the contractor.

1. Sending in a sample that is less than ideal visual quality

When manufacturers validate a process, they just want to prove that the process is capable of making the product according to the outlined requirements. Sometimes, this sample doesn’t look visually perfect. And when the customer receives their product they are taken back.

The problem isn’t in the quality. In this case, the expectations were not set properly for your customer. You have opened the window for the customer to question the quality of your work. When you go to explain that it will take some time to get a sellable product, then a bit of dissatisfaction creeps in. Is this partnership going to work out? Can this company deliver on its promises?

That of course is for you to answer. But it helps when you establish the expectations upfront.

2. Showing off a finished product does not mean the work is done

Let’s say that the new project has gone through the initial inspection and the resulting parts look great. The first article samples are shipped to the customer, and they are ecstatic. They are ready to place a purchase order for their first production run. Oh, by the way, they need thousands of pieces by the end of the month. HOLD THE BUS! There is still some work to be done to ensure that the process is repeatable and that the equipment is production-ready. They may say “what do you mean, you already sent us good parts!?”.

This is where the iceberg analogy and the idea of above/ below the surface shows its teeth. Above the surface, we have stellar results. The product looks and works great. In the customer’s mind, the majority of the work is complete. But beneath the surface, the process that goes into making that product has to be refined. This often involves training, experimentation, oversight, data capturing and analysis, capital investment, and a whole lot more. Here’s the point – just presenting the results means leaving out everything it takes to get there.

3. The infamous design change midway through the project

There’s nothing that screams “we don’t know what we want!” like a down the value-chain design change.

Now, prototyping is part of the game, we get that. But the amount of work that goes into diverting from the original plan, especially when there are huge capital investments involved, is daunting. While the customer just wants what they think works best for them. But these changes are not subtle, cheap, or quick. These are the types of changes that can make a project stop in its tracks, or at least slow it down.

4. Costs that are hiding in plain sight

Quoting a new project isn’t a straightforward matter. What makes it complicated is when the project budget rises as more labor, equipment, overhead, and time is introduced. Focusing solely on the end price for the product highlights the 10% and completely ignores the work done underneath the surface – the “body” of the iceberg. Below the surface, there are other costs that appear as the work matures. But manufacturers don’t want to spin customers around by scavenging every nook and cranny for pennies. Instead, they often spread these costs across different areas to present a more digestible bill. Some of which are not even passed down to the customer, even if it’s at the contactor’s loss. By the way – we must make some money too.

5. Waiting at the shipping dock wondering when parts will show up

From the time the purchase order is processed until the product is on the truck – manufacturers are diligently working. But sometimes there is a bottleneck in the process that puts us in a holding pattern. It would be a Shakespearian world if this was something we can control but ultimately it is not. Because of supply chain interruptions, labor availability, vendor-driven pauses, and other things that cause unplanned downtime, there is always a chance we miss the deadline.

Here’s the thing – we can’t control everything but we can at least communicate. More times than not, the customer would rather know that a machine had to be sent out for repair and the lead time will have to be adjusted than to be left out in the dark.

Addressing the problem going forward

So how do we address these key points? The answer isn’t simple, but it can be done through a roadmap for continuous improvement. Start with a detailed schedule to set expectations from the start. This will help keep your team and customers on the same page. Next, bring your customers in on the process and educate them. Show them the work that goes into creating the product and they will be more understanding when you want to solidify your processes. Another thing you can do is be a more effective communicator. Communication is always a challenge, but by improving this aspect of your business your customers will be better informed. Not only that, but they will appreciate your willingness to be transparent. And finally, deliver value anytime you talk about costs. When you focus only on price and don’t show everything they get in return, then customers will fight you on costs.

Most engineers approach risk management with a ho-hum attitude.

If you’re an engineer, then this probably isn’t your favorite task. For some, risk assessment is just a formality – a report passed around by different departments. So, you might take this routine easy, letting minor issues go untethered. This causes problems as those minor issues stack and becomes larger. As a result, the organization suffers a loss in both time and money.

Instead, you could avoid this with a well-executed risk assessment.

By addressing high-risk areas through a project’s lifecycle, you can save a company from disaster. This takes the hand of a seasoned engineer.

Are you about to launch a new injection molding project? Want to see how our team performs its risk assessments? Then buckle up! We’ll take you through our 9-Step Risk Assessment Process for assessing a new project request.

1: Part Design

For starters, most injection molded products follow a set of design rules. We call these Design for Manufacturing Principals or DFM. In essence, products that follow these guidelines are easy to produce and offer other molding benefits. This includes reduced scrap rate, less material use, and quicker production cycles.

The first thing we do is evaluate a drawing (or CAD) we receive for manufacturability. This process starts with looking at the product’s geometry. We do this to identify any details that are “difficult to mold”.

For example, wall thickness is one common design flaw we find in drawings. A thick wall can cause product deformation in the form of sink. And deformed products are destined to fail in the field, so we don’t want to encounter that issue!

Similarly, critical dimensions with tight tolerances are tricky. This is because of plastics’ ability to shrink. To clarify, as the product cools it shrinks based on the material’s properties. As a result, the product can shrink past the print’s callout. Of course, this is harder to avoid but doesn’t prevent us from making the product.

Instead, a subtle design change in the early stages will negate this issue before incurring avoidable costs. The result: good product with minimal engineering costs.

If you’re unsure about your part design, you can work directly with us to work out any questions you might have. Alternatively, you can look at conducting a mold flow analysis– a program that simulates how the design will fill in an injection molding environment.

2: Materials

Not everyone is an expert in material science, and you don’t need to be. But having a good understanding of the material you are working with goes a long way towards reducing your risk. You should identify whether the material you want to use is compatible with the application. Otherwise, the consequences of purchasing the “wrong material” can set your project back financially and timewise.

One of the obvious questions you should ask yourself is: “Does this material’s physical and chemical properties meet all my engineering requirements?” In other words, you’re asking yourself whether the material will work under the product’s normal operating environment. You can’t run plastic that has a low melting point in a high heat environment… It’s going to fail. But you already know that!

While that last example might be a no-brainer, some questions don’t come as easy. Here’s our top 3:

Material Availability – What does the availability of this material look like? Supply chains are as fluid (and unpredictable) as ever these days. Also, some materials require a Minimum Order Quantity (MOQ) which can impact the cost.
Process Compatibility – This comes into play with secondary processes such as over-molding or ultrasonic welding. Does the material you selected play well with others?
Dimensional Stability – Does your product require tight tolerances? Well, a well-known quality of plastic is that it shrinks! The amount that plastics shrink varies between each material and each formulation. Just something to keep an eye on!

Ultimately, your best resource for plastic is a materials supplier. Our network of materials suppliers can offer design guides, datasheets, spec sheets, and more. We often involve these suppliers early in the process just so we have all the necessary information in hand and can eliminate potential risks.

3: Tooling

When looking at risk assessment for a new mold build, we exercise a lot of information from other areas that were covered in the previous sections. This includes part geometries, material selection, and labor usage (see automatic molds vs operator-required molds). The goal at this stage is to confirm that the mold’s capability matches the project’s requirements in terms of value, volume, and efficiency.

For instance, one way we facilitate harmony between reality and expectations is through production volume. If your annual production volume is less than 25k parts, then you’ll likely want a prototype quality tool. In contrast, if you’re looking at +1 million parts, you’ll want to upgrade into production tooling to avoid doubling down on your mold investment.

Another great point is building the mold with the right materials and features. When we talk about steel materials, we look at the chosen material’s physical and chemical properties. You don’t want a glass-filled material running thousands of shots in an aluminum mold because it will wear faster. With mold features, you can underestimate the labor cost of a mold with multiple hand loads and other manual-intensive features.

Plastics Plus manufactures all its tools to SPI specifications. And because any tooling built and retained is maintained at no cost to the customer, it is in both of our interests to conduct a full risk analysis and mitigate any risks before turning on the build.

4: Labor

Labor might not strike you as a risk factor. But the truth is – labor can be sneaky and costly when unaccounted for. There are a few circumstances where we try and address any labor risks, so let’s dive a bit deeper.

Part and Tool Design: good manufacturing design principles will tell you that fewer components in any given assembly are ideal for manufacturing. How does this relate to labor? Well first, more components will require more labor-intensive activity like degating, deburring, trimming, machining, welding, and more. This introduces the possibility of variation and mistakes in handling the product.

Then, we must consider the risk with the actual assembly of the product. The further along down the production lifecycle, the more valuable the product is and the more expensive it is to lose on defective parts. Ultimately, we look at the risk associated with performing the entire assembly along with the possibility of not having enough people to do them. This is especially an issue with the current labor shortage.

For tool design, we look at whether the tool is automatic or not. The question we ask is “does an operator need to stand in front of the machine to do XYZ”. If not, then the machine can run without operator supervision (aka does not use labor resources). If the mold has multiple features, like hand-loaded inserts, then that requires much more labor.

Physical Injury: Good Manufacturing Practices (GMPs) and OSHA standards cover most common workplace accidents, and we value injury prevention as much as any manufacturer. But as we mentioned above there are inherent injury risks present with labor. And the injury doesn’t always happen at work. An injury can occur on the factory floor, or it can occur outside of work during a pickup game at the YMCA. Either way, injuries are a risk we must consider as it contributes to a strained workforce.

*Just a note: we rotate positions on our production floor for this reason. It’s unlikely someone will sustain a serious injury, but it’s a risk that is still present.

5: Equipment

Equipment failure isn’t something we run into often. However, the inherent risk with unplanned downtime due to equipment failure must be considered in the risk assessment. Unplanned downtime due to machine failure or mold damage happens for a few reasons: One – the equipment runs past its expected lifetime and requires repair or replacement. Two – the machine does not function as intended because of numerous factors. To prevent the latter, we test and validate our processing procedures to reduce human-caused errors. Furthermore, we keep a detailed maintenance database to check the pulse on all our equipment.

Another risk we consider is sourcing a new piece of equipment. For example, a new project might require a minor investment in equipment such as a fixture. Another might require us to buy an entirely new piece of production equipment like a heater or dryer. In either circumstance, we are at the mercy of our supplier. If the lead time on that equipment is extensive that poses a huge risk to the project’s timeline. Under those circumstances, the cost due to lost time can result in thousands of dollars. Therefore, we do our due diligence to ensure that we receive and can operate the required equipment for your project.

6: Packaging

By working with Plastics Plus, you have the option to produce a finished, packaged product. In other words, your product can be molded, assembled, and packaged all under our roof and shipped to you ready for market. This is a great advantage for you as the product owner, but it doesn’t come without risk.

The risk in packaging is a combination of a few other risk areas that we’ve covered in this article. For example, let us examine the packaging equipment. A complex packaging machine can do a few things at once: unroll, print, open (with air), and seal the package within a single cycle. Any variation in this process will impact the quality of the packaging and potentially the product. And any machine failure will result in unplanned downtime. In either case, the result is a loss of time and money.

Now let’s look at this from a materials standpoint. As with most supply chain constraints, not being able to source the packaging is the primary risk. The secondary risk is sourcing poor-quality packaging that doesn’t meet either of our standards. If we added a third risk, it would be scrapped packaging. All three of these situations pose a risk to our operations. But more importantly, it poses a risk to your bottom line which is what we are aiming to improve in the first place. Before we jump into one more area of packaging risk, we should remind you that our quality system is designed to prevent the poor product from ever reaching your doorstep. Thus, you can be confident will address any major concerns upfront.

No one likes to be blindsided by poor foresight.

Since we mentioned shipping to your doorstep, we should address the risk with shipping products. When we ship products via courier there are a few things that can happen. For instance, products on long-hauls can be damaged on their route because of poor handling. Nevertheless, we contract with major courier services to ensure that a professional is handling the product. Ultimately, the risk here is minimal but needs to be considered as part of our process.

7: Application

Application, or the end-use of the product, is one of the most important portions of our risk assessment process. We need to collect as much information on the use of the product and the environment as possible. During our initial conversations, we will expect to learn exactly who the end-user is and what the impact of the product is. Furthermore, we will want to identify the level of safety (or danger) for the user. On a similar note, we will consider whether the product is fit to function in its intended application.

For example, products that come into direct contact with a medical patient (such as a cannula) carry a higher risk factor than a plastic clip. Similarly, if the component is critical to the operation of an assembly or device (such as a CPAP) then the risk is also high.

Comparatively, if the product does not interface with the user and has low criticality then the risk factor is lower. Nevertheless, we still evaluate whether the product can be successful in its normal operating environment. Just because the risk for injury or death is low, we still want to prevent product failures. In this case, we’ll look at the fit and function of the part from an engineering and materials standpoint to identify any red flags. Ultimately, it is your job to determine whether the product is fit for purpose.

For review, we covered three application risks in this section:

Risk to the user
Risk of criticality
Risk of fit for purpose

Next, we’ll cover risks associated with compliance and quality requirements.

8: Regulatory Compliance

Regulatory compliance isn’t necessarily a risky undertaking for most projects. FDA compliance, GMPs, and other regulatory/ statutory requirements are handled primarily on your end. But we often abide by the same requirements to give our customers a seamless experience. However, these requirements prove to be more stringent for some products than others. Some of these falls outside of our capabilities, namely controlled molding environments and ISO-certified clean rooms. Under those circumstances, we avoid risk by turning the project away. On the other hand, we assess projects within our capabilities and determine the risk of falling out of compliance. All things considered, our quality department ensures that our party abides by all requirements laid out by you, the customer.

9: Special Quality Requirements

Validation is a staple in any robust Quality Management System (QMS). This is a multi-step, cross-departmental function in most manufacturing companies. It proves the capability of the methods machinery used to produce, measure, and test the manufacturing outcomes. In other words, the quality requirements set forth by the customer are fulfilled through validation procedures.

When we consider the risk inherent in those quality requirements, we look at the capabilities of our staff, equipment, and processes. These risks are like those present with regulatory compliance in that every product is a bit different. The first thing to consider is whether we can meet the proposed quality requirements. Some products carry tight tolerances in their drawings, critical dimensions that are unavoidable. Although we specialize in close-tolerance injection molding, we encounter some dimensions that are outside our capabilities. Once we establish competency to meet those requirements then we show our proof in the pudding. Explicitly, we’ll run our tests (IQ, OQ, PQ) and conduct others as required (PPAP, MSA, DOE, etc.).

If you want more information about our quality procedures, you can follow the link here.

Conclusion

By now, you should have a grasp of all the elements of proper risk assessment. Congratulations! You’re on your way towards approaching risk like a seasoned pro.

Good luck with your next project! Contact us if you need help conducting a full risk assessment on your next injection molding project.

Want more engineering tips? Follow our newsletter by clicking the link here and get tips from our engineers delivered straight to your inbox.

Introduction to Plastic Living Hinges:

A plastic living hinge is a part design feature that uses a thin plastic material to join two larger plastic bodies of the same material. In other words, a living hinge is an extension of the common material between the two plastic parts. These types of hinges are common features in product design for several reasons. For instance, they are easy to manufacture, reduce production costs, and improve the end-user experience. Take this for example:

Remember when you had to unscrew the cap on the ketchup bottle before you doused your hot dog in tomato goodness?

With plastic hinges, the condiment bottle manufacturers removed a simple inconvenience. They replaced the screw top with the easy-to-use, pop-off white caps we know today. A feat in mechanical engineering if you ask me. Yet, this was not the only way living hinges revolutionized plastic products. There are more examples that span over many different industry segments. We’ll get to those shortly.

In this article, you’ll learn what a living hinge is and how it is produced in a manufacturing environment. Also, we’ll highlight the features and benefits of using them in your part design. Our process involves using thermoplastic materials, the main ones being polypropylene and polyethylene. By the end of the article, you should have everything you need to design a living hinge for your next project.

What is a Living Hinge?

The definition of a living hinge is a thin section of plastic that connects two large plastic pieces. In our ketchup cap example, this would be the base of the cap and the lid. The two of which are joined by a thin and flexible plastic- the hinge. In this case, the cap uses what is called a butterfly hinge. There are four types of living hinges that we’ll talk about later in the post.

What are living hinges used for?

Living hinges allow for the two aforementioned plastics pieces to rotate along a thin hinge line. This gives the part greater rotational mobility – usually 180 degrees or more. This mobility is one of the prime reasons why designers love to use living hinges. For instance, some applications are designed around rotational mobility being the core feature because it makes the product easier to use. Ultimately, this improves the overall product’s look, usability, and function.

Aside from improved usability, a living hinge also requires fewer manufactured components. For example, a container that uses two-piece hinges requires multiple parts for the hinge to work. Unlike the traditional hinge, the living hinge is an extension of the container itself. The result – a living hinge has fewer parts to assemble and simpler tooling requirements. These two factors eat up a large chunk of the manufacturing costs. Overall, using a living hinge design has three key features:

To summarize, the main reasons that living hinges are used for are:

Improving a design
Reducing manufacturing costs
Giving the user a better experience with the product

Why should I consider a living hinge for my part?

If you’re thinking about using a living hinge versus a traditional hinge there are a few things you need to consider. One thing is how much the design affects your manufacturing costs and process. If your product is compatible with a living hinge design, then you might be able to save some money. However, the opposite is true that a poorly designed hinge will lead to more manufacturing costs down the line.

Another consideration for living hinges is how it will affect your customers. A well-designed living hinge can change the way customers view and use your product. However if the design doesn’t make the product easier to use, more affordable, or look better, then it is best left alone. Ultimately, you should consider a living hinge if you believe it will improve how customers view and use your product.

Now, let’s talk about the benefits of a living hinge design versus other hinges.

The Benefits of a Living Hinge Design vs Traditional Hinges

There are three main benefits from using a living hinge design:

Less manufacturing costs – In most cases, a living hinge is less costly than its traditional counterparts. In the context of injection molding, a traditional hinge would require cutting another cavity into the mold plate. In other words, you would have to make accommodations for an additional component for both manufacturing and assembly. On the other hand, you might even cut a check for an entirely separate tool to produce just the hinge(s). This will quickly add to your piece part price even if the tool build is simple. With the living hinge, the entire “assembly” can be made using one to two cavities, so no extra costs. Your tooling cost would be less expensive because you would also eliminate an assembly step.
Better user experience– How a customer experiences your product is every bit as important as how it’s made. We’ve discussed the consequences of a poor design, but what about a good design? There are many opportunities where a well-designed living hinge can change the way customers view a product. The ketchup bottle cap was an obvious one because it changed the way manufacturers made condiment bottles. Now, Heinz was already a market leader in this category. But a design like that could help a lesser-known company become a fan favorite!
Durability and flexibility– We’ve talked about the ketchup bottle cap many times now- Are you worn out from it? Well, the cap is still going strong, bending at the hinge with exceptional rotational mobility. And that’s exactly what it’s made for! A living hinge has an incredible lifespan even after it’s activated millions of times.

Now that we’ve gone over some of the main reasons why designers use living hinges, we’ll start talking about the characteristics that make these designs so adaptable.

What Are the Characteristics of a Living Hinge?

Performance characteristics

Application – Living hinges by nature are adaptable to many designs that utilize a hinge. This is especially useful in prototyping, where you might be testing different hinge designs.
Visual – The properties of their parent material – polypropylene – allows living hinges to have a smooth and clean look. You’ve probably seen the many colors of bottles down the shampoo aisle at the store, so almost any color is achievable.
Chemical Resistance– Although polypropylene has less chemical resistance than other plastics, a plastic living hinge is more resistant than metal or ceramic. However, below-freezing temperatures (32F) could cause the hinge to become brittle.
Durability – Durability is not an issue for this type of design.
Flexibility – As explained before, the 180-degree rotational flexibility of the hinge is one of the main reasons it is successfully deployed.
Friction Reducing – When the pivot or hinge line involves two or more pieces there is more friction between the two parts. But with a living hinge, the friction is all but eliminated.

While this list characterizes living hinges in a general sense, there are different designs that each offer a certain advantage. Let’s talk about those different designs in this next section.

Types of living hinges

Straight/ Flat living hinge – A straight hinge is a single or series of hinges that fall along a single axis. There are two types of flat hinges:

1. Long continuous– These are common with plastic containers- like pencil boxes and clamshell containers. In this case, the hinge connects two long plastic pieces using a single long hinge line.

Short continuous- The short continuous hinge is common to shampoo bottles. This hinge is shorter and uses what’s called a plastic stop- a piece of plastic that stops the hinge’s rotation at 180 degrees.

Butterfly living hinge – Snip, snap! The butterfly hinge design allows for snappy lid opening and closing. However, because this design has a spring-like function there is a limited range of motion. For example, the lid can only flip to the 90 degrees or 180-degree position depending on the design.

Double living hinge- Now this is unique, a double living hinge! These designs create a gap between the two plastic bodies using two straight hinges separated by a narrow open section. Not to mention this also allows the hinge to rotate a full 360-degrees. A good example of this is an old CD case.

Bi-stable living hinge – A bi-stable living hinge uses three separate hinge sections to perform strong open and closing action. This is very similar to the short continuous flat hinge, except with more hinge. In other words, the bi-stable hinge is stable (or a firm) in both open and closed positions.

Now that you know there are different options for designs, your next question is probably- How are living hinges made? In the next section, we’ll go deeper into the manufacturing techniques used to make a living hinge. Keep in mind, we’ll be focusing on plastic manufacturing.

Manufacturing Techniques To Create Living Hinges

Subtractive manufacturing- CNC Machining

In the prototyping stage, there is no better way to test a design than CNC machining. With a CNC you can machine the plastic down to a couple of thousandths (of an inch) on the hinge. However, polypropylene is notorious for being stubborn and might produce some rough edges. For this reason, you would need to switch to the next manufacturing method when you’re ready for production.

Injection Molding

Injection molding is our bread and butter at PPT, which is why we know how to make living hinges this way. For one, this method is easily the most cost-effective and will produce parts at the highest rate. Second, injection molding produces the most consistency in terms of quality and variation. Therefore, once you nail down your design for manufacturability you can produce consistent parts at a fast clip.

Additive Manufacturing – 3D Printing

3D printing is another popular prototyping method that designers use. In fact, 3D printing allows you to see how a design functions before ever going into production. With this in mind, you can test and adjust your design without sinking thousands of dollars in tooling. The downside to 3D printing is its limited production capability. This is where injection molding comes into play for the long run.

Types of Injection Molding Materials Used For Living Hinges

Polypropylene (best): Polypropylene (PPE) is a soft, flexible plastic that is best suited for this type of application. This material’s properties allow for that true rotational mobility of 180 degrees. And the material is flexible enough that it won’t snap, crack, or rip at the hinge line. Ultimately, this is the material you’ll want to stick with or change to if you want to design a living hinge.
Polyethylene: Polyethylene is also a good material to work with. Here, you have one main option: High-density (HDPE) material. The high-density material is thick but easier to machine on a CNC. Furthermore, the hinge line can be made thinner to allow for increased rotational mobility.

Conclusion

In summary, a living hinge is a quality design that can improve the usability and flexibility of your product. And you will benefit from lower manufacturing costs and deal with fewer assembly parts. If you’re curious about how a living hinge design works, or you have a design of your own you would like us to manufacture, give us a call! We’ll help you get up and running in the presses in no time.

What is the question burning in the back of the mind of manufacturers today? The same as it’s been for decades – how do I reduce my costs and increase productivity? With the mix of labor force struggles, high demand for products, and strained supply chains, maximizing efficiency is more important than ever. That is because time is a limited resource and already spread thin in most factories. So, how can we maximize our use of time to bring costs down and produce more? One way is to design an efficient assembly process with a one-piece flow.

In this post, we will introduce the concept of one-piece flow assembly lines. We will discuss why this process is more efficient compared to other assembly processes. For example, we will focus on the difference between batching and one-piece flow. Additionally, we will link to a video that illustrates how much time you can save with this process.

Ready. Set. Assemble!

What is One-Piece Flow?

Flow is the movement of a product from one operation to the next in a value stream. With a one-piece flow, the goal is to plan the workflow based on the products’ needs while eliminating wasted movements. In other words, with the one-piece flow, you want to cut touches that interrupt workflow and that aren’t value-added. Ultimately, this allows you to move between operations without work-in-process (WIP) between them.

To demonstrate, some real-world examples of continuous flow are flowing water and wind. These two elements flow continuously until they are restricted by obstacles (rocks, trees, structures), constricting their flow. Below is an illustration of this happening in nature.

As you can see from the illustration, the canoes can travel down the river with ease when there aren’t any obstacles. When we introduce objects that interrupt that flow our adventurers have a much harder time traveling downstream.

Continuous flow in nature

Bottlenecks:

On the production line, this creates what we know as a bottleneck. A bottleneck is a process in an assembly line with limited capacity that affects the capacity of the entire line. In other words, a bottleneck constraint occurs when there is too much work/ supply at a specific point in a process. Ultimately, a bottleneck holds up the rest of the operation up and down the value stream. This results in longer delays and higher production costs.

Where Did One-Piece Flow Originate?

Single-piece flow comes from the lean manufacturing practice of just-in-time (JIT). The well-known car manufacturer- Toyota -pioneered this idea in the mid 20th century. With just-in-time, manufacturers produced components only as needed and nothing more. In other words, with a one-piece flow, the manufacturer delivered a product only when the customer demanded one.

This lean system resulted in many manufacturing revelations. For one, it helped standardize many processes and workflows. But more importantly, one-piece flow helped cut inventory build-up and cost. Because of this, manufacturers were able to fill orders at the rate of customer demand without having to back stock pallets of products. All in all, by optimizing their workflow manufactures reduced their inventory cost, used time and resources more efficiently, and increased their output.

Why is One-Piece Flow Better Than Batching?

Batching is the process of finishing one operation for a whole batch of pieces before moving on to the next step. For example, for a batch of 10 parts, an operator would complete step 1 for all 10 parts before moving onto the next step. Most of those unfamiliar with lean manufacturing would accept this as common sense and run with it. Some would even argue that it is an efficient method.

Not so fast!

What happens with batch processing is this massive pile-up of inventory between each station. We know this as work-in-process (WIP). And when there is WIP someone is waiting for that process to finish. That someone could be the next person on the line, or a customer waiting for their product.

Waiting time = wasted time.

Check out this illustration showing the time-saving between one-piece vs batch processing:

In this example, when we use single piece flow we reduce the assembly time by 40%!

Let’s break down what we are seeing above in batch processing:

Operator 1 (Blue) has to complete Step 1 for all 10 parts in the batch. She then passes all 10 pieces to the next operator.

Operator 2 (Orange) gets her hands on the batch after patiently waiting. Now, she must complete Step 2 for all 10 pieces. There are now 10 parts that are WIP. * Side note- If this operation were to continue past these 10 parts there would actually be 20 parts in WIP and 30 in the next step.

Finally, Operator 3 (Green) initiates Step 3. After the first 60 second cycle, we finally have 1 finished good. But, it has taken us 21 minutes to complete just 1 part! At the end of this operation, they will have spent 30 minutes on these 10 parts.

Now, let’s move over to the single-piece processing graphic:

Operator 1 (Blue) takes one piece and completes step 1 in 60 seconds. She moves the finished part to the next operator and grabs a new part. She’s moving fast!

Operator 2 (Orange) ‘pulls’ the first part to her station and finishes her step in 60 seconds. Again, she moves the part onto the next station and pulls a new piece. We’re on a roll now!

Operator 3 (Green) now has the first piece. There are a total of 3 pieces that are WIP and 7 that have yet to be touched. But, once this step is completed they will have completed their first finished good in 3 minutes! Also, they will now churn out a finished good every 60 seconds because there is a continuous flow. After just 12 minutes, the second line has finished their batch of 10 parts.

See the difference? If this wasn’t clear enough, check out this animation.

Now that you know what you (might) be missing out on, we’ll show you how to set up your workstations for one-piece flow.

How To Achieve Continuous Flow

Yes, the one-piece flow has many advantages. Yet, to implement this process you need to meet certain requirements. Without these requirements, the one-piece flow will be near impossible to achieve.

Here are those requirements:

Maintain 100% machine uptime (or as close to 100% as possible).
Work, resources, and time must be divided evenly amongst workstations.
Work-in-process (WIP) must be limited to one item in any station’s queue.
Time to complete a task must be measurable and repeatable.
Time to make one-piece must be scalable to customer demands (takt time).
The quality of resources must be consistent. Inconsistent quality equals poor defect rate.
The operation must be able to consistently produce good results.

Variation is the enemy of continuous flow. To achieve an efficient flow, you have to cut variation from the process. If these conditions above aren’t met, then ultimately you will not achieve a one-piece flow down your value stream. After all, it is possible that your product is not suitable for one-piece flow.

But if you do have what it takes to kick the variation bug, then here are the 6-steps to creating your own continuous flow workstations

6 Steps For Creating Continuous Flow Workstations

Step 1: Design a connected flow

A connected flow involves linking each process step within a value stream. In other words, you can establish an underlying relationship between each processing step in a connected flow. Each manufacturing step is either directly related, or related by a pull system like FIFO. Ultimately, the goal of this relationship is to move the product from step to step with little to zero waiting time.

Step 2: Determine whether the workstation is product-focused or mixed

Basically, the difference between product-focused and mixed is the number of products that occupy that workstation. For instance, if the workstation focuses on one product then you can focus on that process. However, the demand for this product must be high enough to maintain a continuous flow.

If there is a mix of products that need assembly at this workstation, then the rules change a bit. For example, if the workstation has to accommodate product A one hour and product B the next, you’ll need to use a mixed station. With a mixed station, the goal is to minimize changeover time. Changeover time is the time between the last good product run and the first good product of the new run. As a general rule, changeover time must be less than one takt time.

Step 3: Calculate Takt Time

Takt time– a measurement of customer demand expressed in units of time. Takt time allows you to keep a pulse on your customers’ demands without under or over-producing products. This is another concept of lean manufacturing and just-in-time where the customer only receives a product when they ask for one. Ultimately, this drives production and inventory costs down.

To calculate takt time use the following formula:

Takt time= Available work-time per shift / Customer demand per shift

Step 4: Determine the processes and time required for making one piece

Step 4 involves conducting an extensive time study on each of the individual processes within the whole operation. First, you need to identify each step in the assembly process from start to finish. Then, you will want to follow a single product through the process from start to finish. Record the time it takes to complete each step as you move through the process. Once you finish, go back through and time each step repeatedly. From this data, take the lowest repeatable timestamp and use it as your baseline going forward.

Can your recorded times match up to meet takt time? If not, you may need to reevaluate your processes and/or equipment.

Linkable content – How to conduct a time-study.

Step 5: Create a lean layout using elements of 5-S

Creating a lean layout is a difficult, but necessary activity. The goal at this stage is to limit wasted movements within the work cell. For example, placing equipment and material at the point of use is a great way to cut wasted movement. On the other hand, if the operator must turn around every 5 seconds to grab a tool then they are wasting movements. In short, wasted movement slows down the line which creates more WIP- a cardinal sin in this discipline.

Another great way to cut waste is through the workstation’s design. The most common design, and perhaps the best, is the U-shaped workstation. This gives an operator full access to resources with limited movements. Yet, there are some instances where a U-shape is not possible due to space constraints. You can experiment with other shapes to find out the best for your situation.

Linkable content: Case Study- Why the popular video game Overcooked is a perfect example of bad cell design.

Linkable content: What is the 5-S methodology

Step 6: Balance the workstation and create standardized work instructions.

The last step is to balance the workstation and deploy a standardized process for splitting up the work time. For example, our earlier segment showed a 3-step setup with each step requiring 60 seconds of work-time. The entire process takes 3 minutes to complete, which can be split up between 3 operators for balance. If we added an operator, then we would split the time amongst the 4 – equalling 45 seconds each. Similarly, we can subtract an operator and split the 3 minutes in half, 90 seconds each.

Again, the way to balance the cells depends on the number of steps and how much time each step needs. There is a formula that tells you how many operators you’ll need to be successful. That formula is shown below:

Number of operators = Total work content/ Takt time

Ex: 720 seconds / (28800 seconds in a shift / 100 parts per shift demanded)= 2.5 operators

Oops! We have half an operator leftover! This is called an inconvenient remainder. With these remaining operators, it is difficult to balance the assembly line. You can reallocate these operators/ activities to resource management to balance the line. Or, you can reevaluate your value stream to make it more efficient. To do this you need to cut steps out of the operation or reduce the time needed to complete the longer steps.

In conclusion, one-piece flow is one of many ways to optimize an operation. Most of the time, continuous flow is achievable with one, if not all value streams. But, that is if you have the right resources. If not, then it is important to continuously improve processes to try and achieve this flow. Ultimately, this is the way manufacturers can increase output, reduce costs, and keep customers stocked. If you don’t have the resources, for whatever reason, then working with a contract manufacturer would be the best course of action.

Older Posts