What Drives Hidden Plastic Moulding Costs Up? Shrinkage, Warpage and Flash

Have you ever wondered why the plastic moulding costs keep rising after you get an estimate? I’ve been in the plastic moulding industry for over 8 years and have seen this issue hit companies time and time again. 

Here, I’ll describe the 3 biggest hidden cost drivers: shrinkage, warpage, and flash. And I’ll show you how to handle them. Learn why each flaw occurs, how they make the cost of plastic moulding goods higher and how you can prevent yourself from going over budget.

What Are the Real Costs Behind Plastic Moulding Defects?

Plastic moulding is the process of shaping molten plastic into a mould under high pressure. Sounds easy enough but the plastic mould itself is only one part of the much larger cost. Other hidden plastic moulding costs are problems such as flash, warpage and shrinking. Shrinkage is the process where components are smaller than intended, due to the cooling and contraction of the plastic in the mould. After ejection, parts could warp or bend. Flash is the plastic that pops out from the seam.

Every flaw means components are rejected resulting in material waste, rework and delays in delivery. The injection moulded plastic will also cost more if your machine has to work extra cycles to replace broken parts. These unexpected plastic moulding costs are due to things like poor mould design, wrong material and incorrect process parameters. For your moulding job to not exceed its overall cost, you must first be aware of these flaws.

Key Cost Factors in Plastic Moulding- Technical Overview

How Does Shrinkage Silently Raise Your Injection Moulding Plastic Costs?

Shrinkage is one of the most baffling problems of injection moulding. All plastics shrink on cooling but the rate of shrinkage varies widely throughout the material. The mould designer must take into account the correct shrinkage rate otherwise parts will be produced that are either too big or too small. This means more machine time and failed batches.

If huge batches have to be re-run, the plastic moulding costs of the injection moulding plastic increase rapidly. Thick walled parts shrink more than thin walled parts, so there will be an uneven distribution of stress inside the component. Improper gating causes uneven packing of the plastic in the mould and aggravates shrinkage. It is far cheaper to prevent shrinkage in the design stage than to repair it in production.

What Factors Make Shrinkage Worse?

• Wall thickness variation: Uneven walls cool at different rates, causing uneven shrinkage.
• Wrong material: Extra design adjustment is needed for high-shrinkage resins such as PE and PP.
• Gate size and location: A little gate will freeze up before it’s time and not let you apply packing pressure.
• Cooling time: Short cooling cycles leave components too hot at the time of ejection, which increases shrinkage.
• Mould temperature: The hot surfaces of the mould increase the shrinkage rate and slow down the cooling.

Shrinkage Rate Comparison by Material

How to Reduce Shrinkage-Related Costs

The best way to minimise shrinkage plastic moulding costs is to work with an experienced mould maker right from the beginning. Huadian Mould Co., Ltd. uses the latest mould flow analysis software to simulate shrinkage prior to cutting steel. This lowers the overall plastic moulding costs of custom plastic moulding, and it also means fewer surprises on the factory floor.

Why Does Warpage Keep Adding to Your Plastic Mould Cost After Production

Warpage is a defect that can occur when a component comes out of the mould. Even if it looks straight at first glance, the component will eventually cool and twist or curve. This is a huge issue, because it is often not caught until the very end, during assembly or inspection. By then, you may have manufactured thousands of defective parts. The three main reasons for warpage are internal residual tension, uneven cooling in the mould, and wrong choice of material.

Higher scrap, inspection labour and rework push up the estimates in the plastic moulding cost calculator. Thicker materials are more prone to distortion than thinner ones. A common characteristic of packed glass materials is flow induced warping. It’s much cheaper to design to avoid warpage than to have to throw pieces away afterwards.

Warpage vs Shrinkage- Key Differences

Shrinkage changes the size of a part and warpage changes the shape of a part. Both of these contribute to the overall cost of the plastic moulding, and both are a function of poor design or process control.

Industries Most Affected by Warpage Defects

• Automotive: Covers/trim panels fit tight, obvious gaps if components are twisted.
• Electronics: Slight distortion can cause failures in housings with tight snap-fit joints.
• Medical: In medical enclosures, where accuracy is a must, warpage can put safety & the seal at risk.
• Consumer Goods: Household Items Thin walled packaging is prone to distortion, which can cause problems with display and sealing.

How Does Flash Secretly Increase the Cost of Moulding Plastic Products?

Flash is the name given to the thin layer of plastic that is forced out during injection from the ejector pins, vents or the parting line. Even if it does no harm, it will cost you real money to take it out. Flash trimming adds more man-hours per batch of products. Cosmetic failures, assembly problems and consumer returns can be caused by flash left on parts. If not kept under control, the cost of moulding plastic parts increases progressively.

Flash is caused by mould surface wear, excessive injection pressure, inadequate clamp force or poor venting. If you don’t keep up with mould maintenance, it will eventually develop a flash. Flash means your mould is approaching the end of its service life and a mould replacement cost is on the horizon. If you catch it early, fixing Flash need not be a big-bucks problem.

Examples: Flash Plastic Moulding Costs in Production

How to Prevent Flash and Protect Your Budget

• Regularly check and repair separating surfaces during mould maintenance.
• Adjust the injection pressure for each material to prevent over-packing the cavity.
• The correct clamp force is determined by the inject pressure and predicted part area.
• Vents blocked – Pressure builds – Flash can occur – Check vent depth and position.
• To begin with, you need to choose a reliable mould maker capable of making tools with extremely tight tolerances.

What Is the True Cost of Moulding Plastic Products When You Add It All Up?

For many the first consideration is the investment in the plastic moulding equipment or the cost of the mould itself. When you factor in such things as maintenance, rework, scrap, delays and defect rates, the real total cost is much higher. A plastic moulding calculator can give you a better idea of total cost. All the factors like material waste, reject rate, manpower for rework, mould maintenance intervals should be put in an accurate calculator.

Unforeseen plastic moulding costs associated with shrinkage, warpage and flash can add 15-30% to the total cost of your project. With a reliable partner like Huadian Mould Co., Ltd. you can stay ahead of these shocks. They provide complete quality assurance testing, mould flow analysis and design for manufacturability (DFM) assessments. The purpose of this method is to remove hidden costs.

Total Hidden Cost Breakdown- Typical Injection Moulding Project

Why Partner with Huadian Mould Co., Ltd.?

• We have been making precision injection moulds for over 15 years.
• The complete DFM analysis before mould production can be used to early detect the shrinkage and warp problems.
• Pricing that’s competitive on generic and custom plastic moulding; no surprises.
• The quality control process is ISO accredited and all moulds are fully traceable.
• To ensure your production plan stays on track, we offer worldwide delivery with fast lead times.

Frequently Asked Questions

What is the average price of a plastic mould?

Three main factors determine the cost of plastic mould, which are mould size, material and part complexity. A basic single-cavity mould typically costs between $1,000 and $5,000. The price tag for complex multi-cavity moulds for automobile or medical component parts can easily exceed $100,000. Get a full DFM assessment first, before you get any surprises in the form of unexpected cost overruns.

• Basic prototype moulds: $1,000 to $5,000
• Medium production moulds $5,000-25,000 
• Complicated, high-volume moulds $30,000-100,000+

How does the shrinkage effect affect the total cost of plastic injection moulding?

Parts that are out of tolerance are a result of mould designs that do not allow for shrinkage. The cost of each rejected part is equal to the injection moulding plastic. Once you start manufacturing, you will have to modify the mould to fix shrinkage. This will increase your overall expenditure. It is much cheaper to predict the shrinkage rate correctly at the design phase.

• Scrap and re-run plastic moulding costs are inflated due to out-of-tolerance components.
• It costs 3 to 5 times more to change a mould after manufacturing has started than to repair it beforehand.
• Watch out, the material you selected has a strong impact on how fast it shrinks.

How can one reduce the chance of warpage in plastic-moulded parts?

The best solution to warpage is to pick the right material that is homogeneous in thickness, optimise the cooling channels and use the right tools for the job. One way to find out warp risks early is to use mould flow modelling before the mould is manufactured. Conformal cooling channels are used to significantly reduce warpage and evenly distribute the temperature.

• If possible, make the wall thickness as uniform as possible.
• Cut steel after performing mould flow analysis.
• Conformal cooling may be useful for complex geometries.

What is the most accurate way to calculate the cost to mould plastic products?

The main factors in a good plastic moulding cost calculator are mould build cost (amortised over the shot life), material cost per part, cycle time, reject rate, manpower and maintenance. With most online tools, they only provide you the bare numbers when it comes to costs for defects. Collaborate with your mould maker to develop a detailed cost model.

• Include the reject percentage in your cost estimate.
• Normally mould maintenance should be budgeted at 1-5% of the annual value of production.
• If buying moulds from overseas, consider the shipping costs and duties.

Conclusion

The answer is simple, fix it preproduction. Working with an experienced mould maker with process expertise and the right tooling can avoid problems such as flash, warpage and shrinkage. All three of these defects are caused by poor mould design or construction and are the main causes of hidden plastic moulding costs. 

If you want to keep your injection moulding plastic costs down and get it right first time, choose an experienced partner. As an associate we have Huadian Mould Co., Ltd. Their quality procedures are ISO certified.