Automation work cells such as insert molding, box filling and in mold labeling/decorating can all be built with greater reliability and simplicity for a lot less money with proper mold design. Even simple automation—such as sprue removal or pick-and-place—can benefit from early discussion about the requirements between the toolmaker and automation supplier.
Hot or Cold Runners
Molds with hot runner or valve gate systems will simplify end-of-arm-tooling (EOAT) design and reduce cost by eliminating runner grippers or vacuum cups and allow for faster part removal. If a mold must have a cold runner, try to sub-gate the parts from the runner and have round pads for vacuum removal, this will eliminate the need for a post mold degating device and save cycle time for other operations. Vacuum runner removal is faster, lighter and less expensive when compared to pneumatic grippers.
When the mold cannot have sub-gated parts a degating station will be needed. A degating station can be as simple as a pneumatic nipper mounted on the robot traverse beam to a sophisticated floor-mounted station with guillotine style shears to cut long fan gates. A simple degating station with two to four nippers can cost as little as $5,000 to $7,000.
Try to keep the gates accessible when designing for scissor-like cutters. Do not have curls in the runner or have runner branches close to the part obstructing the nipper blades.
Box Filling
Mold cavity layout and quantity can be designed to allow easier robotic box or fixture loading. If the shipping container or fixture is defined, design the mold with an even increment of that container. For example, a box holds 40 parts, design the mold with 10, 20, 40, 80 cavities. Forty-eight cavities doesn’t work, a queue station and an external accumulating device will be required adding, cost and complexity along with using additional valuable floor space. Cavity layout also will help with loading a box with parts. Design the mold with part orientation in mind for pack-out.
A boxing conveyor can be used to pack parts unattended from 30 minutes to eight hours. Empty boxes are moved to a loading area, clamped and robotically filled. Then full boxes roll out past the safety guarding and accumulate on a gravity roller conveyor.
Insert Molding
Insert loading is an easy process if the mold is designed properly. Try to keep the insert and removal sides of the mold opposite. Insert on the mold “A” half and part removal on the “B” half. This limits the mold open time, but requires more mold open dimension. Have generous lead-ins for the inserts, and avoid having any obstructions in the path of the end-of-arm-tooling (leader and horn pins).
If possible have the inserts positively located in the mold with little interference. Press fit of inserts will require mold docking and clamping to allow thrust cylinders to push the inserts into the mold. Magnets or a vacuum should be used to hold flat inserts on the mold face.
Mold and insert end-of-arm-tooling docking may be required for very accurate insert placement. The mold simply will have female taperlock style end-of-arm-tooling locators mounted in the insert side of the mold. The use of female taperlocks eliminates the need for clearance pockets in the opposite mold half. These taperlocks should be located close to the part cavity. This gives the end-of-arm-tooling a lot of stability, accuracy and keeps the overall size smaller.
Inserts can be presented to the robot end-of-arm-tooling by a simple manual shuttle drawer with fixtures for a single shot worth of inserts to a vibratory feed system with escapements and staging for an extended unattended runtime. The choice of system depends on how much investment makes sense: the difference could be as much as $100,000 to upgrade from the manual drawer to the unattended runtime solution. However, running three shifts seven days a week could justify this upgrade.
Design the mold to allow for a missing insert(s). Filling an open insert cavity during molding shouldn’t damage or require the cavity to be cleaned out to get back into a production run.
Stack Mold Design
Parts are removed either from the top or side of the mold (usually determined by cycle time). Be aware of mold obstructions—such as stack mold linkages, hot runner control cables and connectors, cooling hoses, etc., which could interfere with the take out robots end-of-arm-tooling. Also keep the cavities inside the tie-bar and leader pins clear of the sprue bar for unobstructed part removal.
Deep parts, like deli containers, should use an air eject system with or without a stripper plate for the fastest removal time.
Mold open stroke also needs close attention. To remove parts with a robot requires more mold open daylight than just eject and drop. The robot mold extraction arm and end-of-arm-tooling must fit in the mold along with the part and core. A molding machine with extended tie-bars may be required to give this open dimension.
Multi-Component Molding
Two, three or four component molding can work with automation just as easy as single component. Two types are manual transfer and rotating molds. Manual transfer requires the robot end-of-arm-tooling to remove the substrate from the first cavity, remove the finished parts from the second cavity and place the substrate into the second cavity (overmold). This type of mold design requires a very large and complicated end-of-arm-tooling, usually a larger robot for payload and extended strokes, and will keep the mold open for approximately 6 seconds—all adding cost and time to a workcell.
The better solution is a rotary table mounted to the moving platen that rotates the mold B half to move the substrate to the overmold position. At this point, the robot can either allow the mold to rotate prior to entering or enter the mold to remove the finished parts, leave the mold and permit the mold to rotate.
This table is either hydraulic or servo activated. In either case, the rotation of this table should be controlled by the robot through the injection molding machine electrical interface. The ejector system needs to be independent for each half of the mold (the substrate and finished part). The robot will permit the finished part ejection while leaving the substrate in place.
A robot can be used if the second or third injection unit is mounted vertically over the fixed platen. The robot is mounted over the clamp end of the injection molding machine on floor stands and either picks parts from the top or the side through the injection molding machine safety gate.
Adding the rotary table may require a larger injection molding machine or extended tie bars to allow for the additional mold open dimension required for the rotary table and robot end-of-arm-tooling.
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Automated Design of Injection Mold, 1. Evaluation and quotation of injection mold products Evaluation and quotation are a comprehensive calculation of the production cost of injection mold products. Only by doing the evaluation and quotation of all production links can the company have an objective revenue and profit. Usually, most companies will construct an injection mold quotation system based on the difficulty of injection mold production, and make a reasonable quotation for the production of a certain plastic or plastic product.
2. Build the product model of the injection mold The current three-dimensional structure of the injection mold is usually built using software such as CAD, CAM or CAE, or the svl format converter existing in the network is used. In the process of CNC machining of injection molds, the computer will program the created 3D model of the mold, including module detection and control, part coding, database management, etc. Enterprises need to code the model and structural design of different injection molds according to complete data parameter information, and improve the design quality and production efficiency of injection molds through the exchange of different module data.
3. Automatic processing and production of mold products. Mold processing and production mainly include the production of cores, mold bases and accessories. The mold core includes movable molds, fixed molds, inserts, sliders and inclined tops, and mold accessories Including shooting tips, flat tips, positioning posts, plastic mold guide sleeves, straight sleeves and square auxiliary devices. At present, in the process of automatic processing and production of injection mold products, Pro/ENGINEER three-dimensional software, UG mold design software, or the secondary development of other plug-in software are mainly used to complete the automatic production of all mold structures and parts.
When designing a product, it’s easy to create something that fits all requirements for the product’s intent without any thought about the manufacturing process. Many times, it might not be clear what manufacturing process will be used to produce the final product.
we are experts in working with plastic injection molding manufacturers. We understand the complications that come with adjusting a design to complement the injection molding manufacturing process. Our Design for Manufacturability (DFM) engineers have decades of experience helping customers make modifications to their designs to ensure their product is manufacturable, cost-conscious, can meet geometric tolerances, and works with the chosen material without compromising the integrity and functionality of the product.
We have put together 6 design tips to help engineers with designing for injection molding.
Tip 1: Do not design a part with non-uniform nominal wall thickness
Varying wall thickness creates uneven fill throughout the cavity
Thinner sections will cool faster than thicker areas causing highly stressed areas where distortion and warping will occur
It is recommended to core out the thick areas to create uniform walls, which will reduce cycle time and plastic usage and improve part cosmetics
Depending on the type of material being used, nominal wall thickness should not vary more than 15%
Tip 2: Do identify possible sink areas and design them out
Sink areas are likely to occur at intersections of a rib and nominal wall where proper design guidelines are not followed
Rule of thumb: Ribs should be a maximum of 70% of nominal wall, but 60% is preferred.
Tip 3: Do create radii on all corners
Sharp inside corners become stressed and outside corners are difficult to fill and trap air
Avoid radii on parting line – causes excess expense on tool build
Adding radii improves fill of corners and distributes stress across a larger area
.030″ radius minimum if possible and if radii are less than .010″ they are not worth adding to design
Place radii at the end of design tree to make collaboration with DFM engineers easier.
Tip 4: Do allow at least 1° draft for part release
For textured surface, more draft is required – follow texture guidelines
If possible, more than 1° draft is better
3° draft or more is needed when parting line transitions from one level to another
Less than 3° draft causes the steel to squeeze together when mold closes making the mold harder to pull apart and creating drag marks on the part.
Tip 5: Do not design bad steel conditions
When envisioning steel required to create part shape, avoid very sharp, tall, and fragile steel conditions
Steel will get hot and be brittle
Steel condition height should not be more than 4x the width whenever possible
When in a corner, one rib is better than two to allow the steel to cool better.
Tip 6: Do not design deep ribs with square corners
It will trap gas and cause short shots
It will be more difficult to eject part.
There are many design elements involved when creating plastic parts for injection molding—design for cost, design for quality, design for assembly, design for manufacturability. And navigating that landscape can be challenging at times. At Protolabs, we provide automated design analysis on CAD models that highlights features in your part design that can be adjusted for moldability. It’s a great design resource to have at your fingertips. To keep those moldability advisories at a minimum and optimize your part design, we created this helpful kit of different injection molding resources.