BMC Injection Molding Process Cycle Time Reduction Sheila Enid Rosado Pérez Engineering Management Héctor J. Cruzado, PhD Graduate School Polytechnic University of Puerto Rico Abstract ⎯ High cycle time is one of most common downtime in molding processes, affecting the output BMC MATERIAL and the efficiency of the area. Equipment and tool Bulk molding compound (BMC) is commonly condition are key to sustain a proper cycle time. This used for small electrical devices. The material is fed project aimed to reduce a 10% of the high cycle time into the machine barrel using a screw. Injection of the three top offenders of a BMC molding process. speed and back pressure defines the part quality For three months, a detailed equipment evaluation regarding mechanical properties or surface was completed to identify machine conditions and appearance. When less force is applied, the higher how they affected the molding process. Once the the mechanical properties will be, the faster the corrections in the equipment were completed, there injection occurs the better the surface will show. was a reduction in downtime of the top three Cycle time determines the proper cure time of the offenders of 67%, 27% and 81%, respectively with entire process. This feature leads a successful regards to high cycle time. molding process when correct parameters are Key Terms ⎯ BMC material, High cycle time applied. Process starts in the injection unit at the reduction, injection molding, injection molding machine, where material is fed and starts the curing process improvement phase. Material is injected to the mold through the barrel to the mold. The clamping unit ensure mold INTRODUCTION will not open during the injection phase. Figure 1 Eaton Corporation Electrical Division is a shows the location of injection unit and the clamping company that is committed to improving people’s unit in a molding injection machine. life with efficient and sustainable power management technologies. Las Piedras plant is a feeder that manufactures components for residential breakers. Eaton Las Piedras is seeking to improve their injection molding process to comply with the increase of demand for their product. Cycle time is part of the Injection Molding process that starts when the bulk molding compound (BMC) material is injected to the mold. Material properties make it perfect for electrical features Figure 1 fabrications, however, is not easy to mold. The Injection Machine Diagram proper parameters are needed to obtain conforming In molding process is recommended to use the parts. In this case, the study is focused on how to same parameters, which means that they must be reduce cycle time on a BMC Injection Molding defined at the validation process. Temperatures process without affecting quality of the finished must be maintained uniform in the range of +/- 2˚C good. [1]. Temperature uniformity is important when molding BMC material, however, a difference of 45˚F can be observed in large-molded parts. In terms of cycle time, the process must consider all the aspect during the injection phase. Closing the mold in a high speed will not allow the gases to scape provoking blisters in the surface of the part. The minimum total cycle time for BMC material is 30 seconds [2]. Figure 2 Reduction in cycle time is a key phase in the High Cycle Time Top Detractors manufacturing process and can be achieved in injection molding. This process is 3 times faster than ANALYSIS compression molding [3]. One of the disadvantages A deeper analysis required a root cause exercise of injection molding are the high cost of the to identify the possible causes of the cycle increase equipment and tool versus compression machinery in the area. and molds. However, the increase in capacity due to The top possible causes of high cycle time injection molding makes this process the preferred to identified by the multi-functional team were below high volume products companies. the category of machine as showed in Figure 3: To implement an improved injection molding • Machine poor condition process, is important to take in consideration the • Auxiliary equipment poor condition following factors: use the less material the process • Obsolete technology allows to have conforming parts; be sure your Mother Nature Man Method Effect: equipment is up to date and your parameters are High cycle time Lack of troubleshooting Machine PM not effective Ambient temperature difference knowledge adequate for the part being mold, make sure your among shifts Material handling Increase cycle time to avoid excesive effort people is fully trained, chose the proper tool design Mold PM not efffective Operator PM not effective or no and material for the process [4]. consistentSet up 2 versus Set up 3 Lack of standard work process Mold conditions BASELINE Cycle time not evaluated by manufacture team Machine conditions Downtime due to high cycle time represented Material out of specAuxiliary equipment poor conditions 19% of the total downtime for Injection Molding Obsolete technology Area. This inefficiency was identified as one of the Machine Measurement Material top areas of opportunities to increase the area output. Figure 3 Data gathered from January 2021 to July 2021 Fishbone Root Cause Diagram identified the top three machines. Figure 2 shows the machines with the highest After the evaluation the findings were: downtime due to high cycle time. The top three • IM-37: issues to sustain clamping pressure offenders of the 300 Ton Injection Machines were during the molding process, the frequency drive IM 37, IM 26, and IM 39. Each machine was in the required substitution to standardize the shot range of 7 to 10 seconds over the standard time size, had issues with the thermolator and the cycle. screw and barrel needed replacement. • IM-26: issues sustaining clamping pressure during the molding process, the frequency drive required to be replaced, and the elevator module were obsolete. • IM-39: had issues with the venting function that a huge improvement with a percentage difference of did not allow the machine to continue with the 9%. However, in September it was observed an process, the thermolator turned off during the increase up to 14% related to mold poor conditions. process not allowing to complete the heat In October a different mold was installed in the exchange process in the mold, the elevator machine, and the data showed a drop in downtime of module was obsolete, and needed vacuum 4%. Machine cycle was reduced from 41 seconds to system. 37 seconds. RESULTS In a collaboration with the maintenance team, the frequency drive was immediately replaced in IM- 37 and IM-26, eliminating the discrepancies during the material shot size while the screw charging process. IM-37 clamping issues were corrected after screw and barrel replacement. For IM 39 the venting function was corrected once a program update was completed to the machine PLC system. Obsolete modules were ordered and are Figure 5 expected to be received by the end of October to be IM-26 High Cycle Time Downtime Trend replaced in IM-26 and IM- 39. Thermolator Figure 6 shows IM- 39 cycle time downtime replacement and new vacuum system were included behavior and trend. Corrections made in August in the Capital Approval Request for 2022. reflected a reduction of 5% versus July results. Figure 4 shows trend regarding downtime due September continued in a decrease trend with a 2%. to high cycle time for machine 37. Running hours This percentage was the lowest observed during during the month are showed in the orange bar, 2021. downtime hours are the blue bars. The line represents the percentage of downtime versus the running hours. After the corrections were made in August the trend was to the downtime decline. The lowest percentage were observed in September with a 3%. Figure 6 IM-39 High Cycle Time Downtime Trend Equation (1) was used to calculate improvement. Figure 4 IM-37 High Cycle Time Downtime Trend (𝑎−𝑏)𝐼𝑚𝑝𝑟𝑜𝑣𝑒𝑚𝑒𝑛𝑡 = (1) 𝑎 Figure 5 shows IM-26 trend of high cycle time Table 1 represents the baseline data prior the downtime. In August the corrections made reflected machines evaluation, while Table 2 shows the machines performance after the improvement were equipment conditions have a direct impact in the done. The average percentage contemplates the total BMC molding process. running hours to normalize the data. When the After project completion, machine performance information in Table 1 is compared with information reflected a reduction in high cycle time downtime in Table 2, it can be seen that a reduction in cycle after correctios were made. It was observed a 64% time was achieved. downtime reduction due to high cycle time in IM-37. Table 3 shows the summary of the results after In IM-26 it was observed a reduction of 27%. IM-39 project completion. The final downtime percentage reflected a reduction of 81% on the total hours down reflects that the project exceeded the goal of 10% due to increased cycle time. reduction on each machine. Downtime reduction on each equipment represented a 2% of increase of overall OEE of the Table 1 Summary Data Jan-Jul 2021 area reaching a 58% which is 3% over the goal. Demand of the product requires to continue with the Machine Cycle time Average Running Average average hours percentage improvements in the area. During the progress of this Jan-Jul 2021 Jan-Jul 2021 Jan-Jul 2021 project, other areas were identified for next projects such as the evaluation of mold PM effectiveness and IM-37 92 513 18% machine PM effectiveness to ensure sustainability of IM-26 76 521 15% the improvements achieved in this project. Finally, IM-39 56 489 12% this information was presented to the Leadership team which evaluated the information and were Table 2 satisfied with the results. Data Summary After Corrections Aug-Sep 2021 REFERENCES Machine Cycle time Average Average average Running percentage [1] Ning Guang Mold & Plastic Co., Ltd; SMC Aug-Sep 2021 hours Aug-Sep Aug-Sep 2021 2021 Mold Solution, (2013), Injection Molding of IM-37 30 468 6% BMC; Available: Injection Moulding of BMC IM-26 44 411 11% (smctooling.com) IM-39 8.5 384 2% [2] Tatara, Robert A., (2017), Applied Plastics Engineering Handbook. 2nd Ed., Available: Bulk Table 3 Moulding Compound - an overview | ScienceDirect Topics Final Downtime Improvement [3] Plastic Mold Solution Provide; (2020), BMC Machine Average Average Final injection molding process for thermosetting percentage percentage downtime plastics; Available: BMC injection molding process Jan-Jul Aug-Sep percentage for thermosetting plastics - Knowledge - Odin Mould 2021 2021 improvement Co.,Ltd (plasticomould.com) IM-37 18% 6% 64% IM-26 15% 11% 27% [4] Rev Part; How to Minimize Cycle Time in IM-39 12% 2% 81% Injection Molding; Available: How to Minimize Cycle Time in Injection Molding | Revpart CONCLUSION Process parameters have an important role in the injection molding process, however, there are other factors that also affect he process. Variables such as