SPRING 1999
Volume 5 • Number 2

• Rapid Tooling: What Is It and What Processes Are Out There?
• Four RT Processes Compared
• Training Update
• Project Engineer added to PTDC Staff

RAPID TOOLING

Rapid tooling (RT) is the term for either indirectly utilizing a rapid prototype (SLA, SLS, etc.) as a tooling pattern for the purpose of molding production materials, or directly producing a tool with a rapid prototyping system.

Rapid tooling processes complement the rapid prototyping options by providing higher quantities of parts in a wider variety of materials. There are several rapid tooling options to pick from depending on time available, material requirements, and part geometry.

Rapid tooling, like other new technologies, has produced confusion and even unrealistic expectations. With all of the hype about rapid tooling, you need to have a better understanding of some of the available processes, their advantages/disadvantages, and, of course, timing. Four rapid tooling processes will be discussed: RTV or Silicone Rubber Molding, 3D Keltool™ by 3D Systems, ACES injection molding or Direct AIM™, and DTM's LR RapidTool™.

RTV (ROOM TEMPERATURE VULCANIZATION) OR SILICONE RUBBER MOLDS
One of the most widely used processes today to obtain three-dimensional simulated injection molded plastic parts is RTV. The process utilizes a master SLA (stereolithography) pattern in the positive form for producing the final part. The SLA master must be fully sanded and polished since the surface finish is critical when making the RTV mold. The mold will reproduce all surface defects left on the master. In turn, it will transfer any imperfections onto the finished part. Even fingerprints will be picked up on an RTV mold and will ultimately appear on each of the parts produced from the mold.

Summary of Process:

1. An SLA master pattern is created (other patterns such as a wood pattern could also be used).
2. The pattern is placed in a wooden box to provide a support structure for the silicone rubber.
3. Silicone rubber is poured into the box, completely covering the master pattern.
4. The silicone rubber is allowed to cure and then is cut to form the cavity and core.
5. A two-part urethane is cast into the rubber mold to create the urethane parts.
6. The urethane parts are then pulled from the mold and the process begins again.

3D KELTOOL™ BY 3D SYSTEMS
Keltool is the process of producing long life, soft tooling quickly and economically for prototype and production runs from one, to hundreds, to even millions of plastic injection molded parts. The word "Keltool" refers to the proprietary powder-metal sintering process, which involves infiltrating a fused metal part with copper alloy. This alloy fills in the voids in the otherwise porous material, producing a surface with the finish and hardness necessary for an injection mold.

Summary of Process:

1. An SLA master pattern is created.
2. Keltool makes a precise, flexible rubber mold of the SLA master pattern without subjecting the SLA pattern to heat or pressure.
3. Keltool fills the rubber mold with its metal mix (powdered steel, carbide, and tungsten) to duplicate the exact detail and shape of the SLA pattern in order to make a "green" part.
4. The "green" part is removed from the temporary mold.
5. Keltool fires the "green" part in a very high temperature furnace to fuse or sinter the metal together and remove the plastic binder.
6. The fused part (about 70% powdered metal) is infiltrated with copper alloy to fill the 30% void space within the porous sintered part - the infiltration is done in a high temperature furnace to produce a dense metal cavity or electrode.
7. Keltool rough machines the cavity or electrode.

ACES (ACCURATE CLEAR EPOXY SOLID) INJECTION MOLDING OR DIRECT AIM™
The ACES process involves building the mold on an SLA system using the ACES buildstyle that is shelled out on the bottom side. This leaves a cavity in the mold halves that can be backfilled with various materials. These materials include aluminum-filled epoxy, ceramics, and low-melting metals. The backfilling process provides a thermal conduit for the heat exchange system, and integrates the cooling system that may be put into the mold halves. The mold halves are mated, aligned, and the part surfaces are finished for surface quality. Using extended cycle times and a release agent, numerous parts can be made by directly injecting the final material into the ACES mold core and cavity halves using a standard injection molding machine.

Summary of Process:

1. Create a 3D model of the cavity and core.
2. Using an SLA with the appropriate resin, build the cavity and core.
3. Backfill the cavity and core with a high concentration of aluminum fillings with epoxy resin.

DTM'S LR (LONG RUN) RAPIDTOOL™
The RapidTool process takes advantage of the multi-material capability of DTM's SLS^® Selective Laser Sintering technology. In the RapidTool process, the material used is DTM's RapidSteel^® 2.0 powder - stainless steel powder of 45 micron average size, blended with a plastic binder. Using a CAD file as input, DTM's SLS process fuses, or sinters, the powder to form the mold geometry. The sintered part consists of metal particles bound by polymer necks, and is referred to as a "green" part. An initial furnace cycle debinds the steel powder, lightly sintering the particles. The resulting "brown" part is set on an alumina plate within a graphite crucible and surrounded by bronze ingots. The bronze melts and infiltrates the part through capillary action.

Summary of Process:

1. Create a 3D model of the insert. Include any water lines, ejector pin holes, and draft.
2. The SLS process is used to create a "green" part. Steel particulate (approximately 40 microns diameter) is used in conjunction with an acrylic binder coating to build a mold insert.
3. The acrylic binder is infiltrated with chemical emulsion, which initiates polymer cross linking.
4. The infiltrated part is nitrogen dried. This step minimizes slump and cracking in large parts, eliminates creep, and provides more uniform shrinkage during the furnace cycle.
5. The polymer binder is burned out during the furnace cycle, and the metal part is sintered creating a "brown" part. The "brown" part is then infiltrated with bronze, creating an insert 60% steel and 40% bronze.
6. Any excess bronze is removed and the insert is sandblasted. Then any external machining of inserts can be completed.

   - Dave Rose, Project Engineer
   - Theresa Warner, Engineer

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Four RT Processes Compared

RTV

Cavity Size:

• No limits specified to date

Tolerances:

• +/-.003 to .005 depending on master pattern tolerances

Delivery:

• 1 to 3 weeks or less (depending on number of tools and number of parts produced)

Approximate Number of Parts:

• 1 to 50+ parts of urethane prototypes
• (typically no more than 200 parts per rubber mold before the mold begins to deteriorate)

Advantages:

• Inexpensive mold cost
• Urethane parts can be colored
• Undercuts can be molded
• Limited functional testing can be performed
• Excellent surface finish
• Soft flexible (45 Shore A) materials to hard durable urethanes (90 Shore D)
• Materials with UL ratings

Disadvantages:

• Limited mold life
• Mechanical properties are typically not as high as production resins
• High piece price

3D KELTOOL™

Cavity Size:

• Inserts (up to 5.90 x 8.50 x 5.75"; 150 x 215 x 145mm)

Tolerances:

• Tool accuracy to within +/-.001 inch/inch claimed (may see up to +/-.005 inch/inch in application)

Delivery:

• 2 to 3 weeks or less

Approximate Number of Parts:

• One part or millions of injection molded parts from a single set of Keltool inserts
• 500,000 to 1 million parts per tool for glass-filled resins

Advantages:

• Reduce costs 25 - 40% compared with CNC machined steel tools for complex geometries
• Faster cycle time due to improved thermal conductivity of 30% copper loaded, A6 tool steel
• Ideal for complex geometries
• Half the cost, one-third the time of traditional tooling for certain applications
• Exact production and engineering plastics
• Outstanding tool life

Disadvantages:

• Licensing from 3D Systems only

ACES or DIRECT AIM™

Cavity Size:

• Limited by size of SLA machine

Tolerances:

• +/-.005"

Delivery:

• 5 to 7 working days

Approximate Number of Parts:

• 1 to 500 plastic parts depending on injected material, part design, and process parameters; mold yield is somewhat unpredictable

Advantages:

• Delivery 5 to 7 work days, therefore multiple molds can be built with varying shrinkages and part designs providing more engineering data for implementation in the final part design
• Low cost compared to other tooling

Disadvantages:

• Short mold life
• Long cycle times
• Part surface finish and accuracy may be inadequate

DTM'S LR RAPIDTOOL™

Cavity Size:

• 5 inches³ is optimum
• 8" x 10" x 4" maximum

Tolerances:

• +/-0.010"

Delivery:

• 6 days from completion of 3D model

Approximate Number of Parts:

• 50,000 to 100,000 plastic parts
• 200 to 500 aluminum, zinc, or magnesium parts

Advantages:

• Raw inserts can be created in less than one week
• High complexity geometry can be created
• Relatively inexpensive compared to conventional machining of complex geometries

Disadvantages:

• Size - 8" x 10" x4" maximum
• Surface finish - 400 Microinches (RMS)
• Tool tolerances - +/- 0.010 to +/- 0.020" over 5 inches; inserts can be machined to +/- 0.005"

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Training Update

At Penn State Erie:
Design of Experiments (DOE) for Injection Molding
Spend time in the classroom, at the molding machine, and utilizing the computer lab to conduct DOEs.

Date: June 9-11, 1999
Where: Penn State Erie, Erie, PA
Instructors: Mr. Bradley Johnson and Mr. David Baird
Cost: $995.00 per person

To compete in today's global market, quality must be designed into both product and production processes. This must carry through at all stages of manufacturing with processes and procedures that facilitate a process of continuous improvement. Carefully designed experiments (DOEs) can remove hindrances to high quality and productivity at every stage in the production of plastic parts. This workshop has been developed to give you practical experience utilizing both the Penn State Erie processing lab and the computer lab (primarily using Microsoft Excel). Emphasis will be placed on in-class interaction and the "hands-on" experience of carrying out and analyzing experiments. This workshop will focus on injection molding, utilizing examples from that process. It will also be of value to those working in other plastic processes and desiring training in constructing designed experiments for plastics.

To Register: You may phone your registration information to (814) 898-6103.

At Penn College in Williamsport, PA:
Extrusion Seminar & Hands-On Workshop
Learn by doing, spending approximately 50% of the course operating industry equipment.

Date: August 10-12,1999
Where: Pennsylvania College of Technology, Williamsport, PA
Instructors: Dr. Chris Rauwendaal and Dr. Kirk Cantor
Cost: $950; $900 (early registration, prior to 7/10/99)

This unique extrusion event combines the content expertise of well-known extrusion consultant Dr. Chris Rauwendaal with the training expertise and modern facilities of the Pennsylvania College of Technology's Plastics and Polymer Technology Department. Dr. Rauwendaal will present course topics in a multimedia format supplemented by printed materials provided to attendees. Dr. Kirk Cantor will lead the hands-on training, comprising approximately 50% of the course. Attendees will operate extrusion industry equipment such as a single screw extruder, twin screw extruder, blown film line, injection molder, melt indexer, and tensile tester.

To Register: You may phone your registration information by contacting the Penn College Plastics Manufacturing Center at (570) 321-5533. For more detailed information, visit the PMC's web site at www.pct.edu/pmc/.

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PROJECT ENGINEER ADDED TO PTDC STAFF

A new addition to the PTDC engineering staff brings experience in high-performance thermoset composite materials such as kevlar and carbon fiber/epoxy.

David Rose, who joined the center in March as a project engineer, is former engineering manager at Composiflex in Erie. Rose also completed the engineer-in-training program at Fisher-Price in East Aurora, N.Y., where he worked in new product development and as a plant engineer representative and a tooling engineer.

In addition to composites, Rose's areas of expertise include new product development for many processes including injection molding, gas-assist injection molding, extrusion blow molding, and resin transfer, as well as tooling for injection, blow, and roto molding.

Rose holds an associate degree in mechanical engineering technology and a bachelor of science in plastics engineering technology from Penn State Erie.