In this article, William Lai, a project engineer of the Design to Value (DTV) Team at Stanley Black & Decker, works with senior product engineer Frank Tsai to perform a series of projects with the help of Moldex3D. The objective of this project is to detect the cause of the cracking problem near the screw boss where a weld line was present.
With the help of Moldex3D injection molding simulation software, they were able to exactly predict the weld line position and enhance product quality. The team was assigned the responsibility of predicting the TPE and ABS bonding temperature and molding conditions in the bi-material design hand tools using a Moldex3D Multi-component Molding (MCM) over-molding simulation. They also designed the appropriate injection gate dimensions and shape to remove a misty surface appearance and cold weld lines in the screwdriver handle grip product. Both were achieved by using Moldex3D iterations of multiple process conditions. This allowed the team to further develop the design to perform more in-depth verifications and structural testing (Figure 1).
Figure 1. The product design process of this case study.
- Cracking close to the screw boss where the weld line is present
- Bi-material design causing additional cost and time delay
- The existence of cold weld line and a misty surface appearance
Moldex3D Advanced Package - to alter the weld line position, enhance the bonding temperature and molding conditions, and improve gate design and core-shift value.
- Optimized molding conditions for the best ABS and TPE bonding
- Changed weld line position to pass the drop test
- Precise core shift value for screwdriver handle grip case
- Reduced cost and tooling time
- Eliminated misty surface appearance or cold weld lines
In order to enhance the surface appearance and the strength of the product, the team employed Moldex3D to study the behaviors of the first and second shot materials and predict the positions of the weld lines.
In the first project, Moldex3D could precisely predict the weld line position, which is also the most fragile area of the product (Figure 2). Thus, the team were able to discover how to alter the inner structure and change the weld line position, to achieve the structural strength they required in a drop test, eliminating the need for expensive design changes during the tooling phase.
Figure 2. Using Moldex3D, production teams can predict weld line positions.
Here, in the second project, Moldex3D demonstrates the over-molding melt front simulation of the first and second shot, which allows users to observe the bonding behavior, melt front, and temperature and make it possible to understand the bonding temperature conditions and further attain the best bonding before tooling commences (Figure 3 and Figure 4).
Figure 3. Moldex3D is able to simulate the bonding behavior of the first and second shots.
Figure 4. Moldex3D Bi-injection Module can predict that the re-melt temperature of the surface is higher than the material temperature difference when the first shot contacts the second shot. Thus, the interface of both shots is expected to be a good combination.
Made from a transparent material, the screwdriver handle grip has extremely thick cross-sections. However, it is not easy to produce as the misty surface appearance and cold weld line problems will inevitably occur (Figure 5). Hence, in the third project, Moldex3D was utilized to simulate multiple injection conditions, using a variety of gate designs to obtain the gate shape and dimensions that could minimize or remove the problems related to the misty surface appearance and cold weld lines.
These issues were eliminated as the plastic flowed very smoothly after the relocation of the injection point (Figure 6). Additionally, the core shift value of the screwdriver metal could be accurately obtained, preventing the tooling problems.
Figure 5. Cold weld line and misty surface appearance issues occurred.
Figure 6. Cold weld lines and a misty surface were eliminated after the injection point was relocated.
After optimizing the injection point and gate dimensions/shape to obtain a correct flow and core shift result with the help of Moldex3D, the team will take the EMC and EMI tests, a reliability test, a CNC sample test, and general assembly verification before announcing the product.
The goal of the DTV team is to drive incremental productivity and reduce complexities for the Hand Tools and Storage businesses of Stanley Black and Decker. Moldex3D has been employed to solve potential tooling or structural problems and simulate the plastic components prior to production. This has allowed Stanley Black & Decker to save on both time, design costs, and product manufacture.
This information has been sourced, reviewed and adapted from materials provided by Moldex3D.
For more information on this source, please visit Moldex3D.