At Westminster Tool, we take pride in being proactive and hands-on partners to our customers. This means not just providing a working injection mold, but delivering one that enables you to hit even your most challenging part print requirements.
As many in the industry know, this is not an easy feat. After years of delayed project timelines and added costs at the end of the project, we decided to invest in researching better, up-front design procedures to define true quality expectations, identify risks, and implement mitigation strategies. We were looking for ways to better identify the manufacturing risks¬—and consequently the quality concerns—before they turned critical and costly. After implementing our new in-depth design process, we found that it saves three weeks or more on the back-end of the project, time traditionally spent debating part success and grooming steel.
It seemed like an obvious solution: Talk about plastic part quality first, then get to manufacturing. But the trickiest part was finding and utilizing the right tools to provide success shot after shot for millions of runs.
Below are 5 strategies we use to embrace defining quality during mold design, and how others can take advantage of them today.
1. 2D Versus 3D Comparison
One of the first things we do at the start of a project is take the provided 3D model and detail all features called out on the 2D print in order to replicate dimensions. This step will flag any discrepancies that may not have been transferred over the years into both versions of files. Taking this extra measure early on ensures we fully understand the dimensions we are aiming for and that the nominal and high/low limits of the dimension are captured correctly.
2. CT Scan Existing Parts
Where part files are not always up to date, sometimes mold files are not either. Any time we are building a capacity tool, we CT scan the current part to ensure we know what is currently successful in the market and integrated with the customers’ existing automation.
Before implementing this check in our design process, we would often build a capacity tool for a customer and build to the existing tool design files that the customer confirmed were accurate. During one molding trial, the parts were sticking, something that did not occur on the customer’s current mold. After sending the existing parts out for CT scan, we realized they had added draft on the existing tool in order to alleviate this, a feature that was not included in the supplied mold files. Unfortunately, this meant reburning geometry, reassembling, and re-sampling the tool, which added two weeks to the total lead time on top of time troubleshooting.
Now CT Scanning helps us identify these kinds of discrepancies right at the beginning, way before molding trials begin.
3. Dimensional Risk Analysis
Part of minimizing cost and time on the back end of a project is identifying the risky dimensions and keeping them steel safe. To do this in a data-driven way, we utilize the SPI (Society of Plastics Industry) tolerance recommendations based on resin characteristics, geometry, and size. These standard recommendations help us flag any high-risk, tight-tolerance areas that we can address during our first design review.
In some cases, such a tight tolerance might not be necessary. In others, it is essential to part function and therefore we must be strategic in our manufacturing plan.
4. Moldex3D Analysis
Westminster Tool performs a Moldex3D simulation for every mold that we build. In our opinion, there is no need to find things out the hard way, especially with today’s simulation technology. Simulations allow us to identify dimensional and quality challenges when the cost to implement a solution is nearly nothing. We flag challenges such as shrinkage, warp, cooling, and any opportunities to improve the mold cycle or overall quality of the final molded product.
On a recent project, our simulations showed the part would likely warp, making it impossible to meet the flatness callout on the part print. We ran the part with a different gating option that reduced the warp by over 50%. The customer agreed to invest in a valve gate hot runner system, which resulted in an upcharge of approximately $3,000 and had no implication on lead time. Had we waited to figure this out during mold sampling, the cost would have been upwards of $8,000 to adjust the plates in addition to adding the new system and would have added anywhere from 3-6 weeks to the total lead time.
5. Design for CPK
When part print dimensions are held to a CPK requirement, special attention is needed to ensure the part and tool are capable of meeting tight tolerances though process variation over the life of the tool. The percent of the plastic tolerance that we apply to our steel tolerance changes based on the CPK requirement.
For example, we may hold the steel to 50% if no CPK is required, and 25% or less if it is. This makes a huge difference not only in the cost and lead time, but also in the ability for us to meet the CPK requirement without adjusting each cavity individually to achieve success.
Collectively, these steps only add about one week to our design lead time, but we have found that they save even more on the back end by ensuring all parties have the same definition of success and a clear plan on how to get there as quickly and cost effectively as possible. On average, a change made during design costs $0-$5,000 whereas the same changes made after first samples can cost as much as $50,000, depending on the change and cavitation.
Engaging in the definition of part quality is just one of the many ways we embrace our customer’s challenges. At Westminster Tool, we specialize in complex Class 101 injection molds with particularly challenging manufacturing dimensions and tolerances. And over the years, our experience with these particularly challenging projects is that access to high-tech testing is only as valuable as its application. We learned that having access to results from tools like CT scanning and Moldex3D simulation are useless if you cannot effectively interpret the data and implement solutions.
That’s why we use these tools not just to better understand the customer’s challenge but to provide them with actionable insights and clear options for a resolution.
To hear more about our experiences with defining quality during design, join us at Amerimold 2021, where our expert team is hosting mini-tech-talks in Booth 217.
