QC-10 High Strength Aluminum Injection Mold

Transcription

1 QC-10 High Strength Aluminum Injection Mold QC-10 Aluminum Molds for high-volume production are emerging as an attractive option for an increasing number of applications because it can reduce cycle times dramatically, speed mold construction, and trim tooling costs. A successful application utilizing a QC-10 Aluminum Injection Mold will typically run 20% to 40% faster than the same part running in a steel mold. This translates into a cost advantage for the molder and customer that is difficult to match. Rapid heating of the QC-10 Aluminum mold during injection facilitates molding at lower injection pressures while the rapid cooling of the QC-10 Aluminum mold enables faster de-molding. If you monitored the actual temperature of a steel mold during a molding cycle and compared it with a QC-10 aluminum mold, the QC-10 mold would show a rapid spike in temperature during injection followed by an equally rapid reduction in mold temperature. For a steel mold, the temperature profile would show a slower, more gradual rise in temperature followed by a gradual decrease in temperature. Studies have shown that the QC-10 LOW Interfacial heat resistance (High Conductivity) will remove heat from the plastic melt even during Injecting and NOT only during the Cooling time of the part. It is important to counter act this fast cooling phenomena of QC-10 by using slightly faster fill speeds and slightly elevated mold temperatures to counteract surface blemishes caused by fast Injection/melt/solidification. However, even with slightly higher mold set temperatures (10-20 degrees) the plastics solidification will occur at a faster rate than with steel molds, therefore result is faster melt solidification and shorter cooling/ cycle times.

2 QC-10 High Strength Aluminum Injection Mold Design Tips QC-10 molds can be designed with many features such as slides and lifters. These are general guidelines and do not constitute limitations but help to plan more economical aluminum molds. 1. Filled Resins such as Glass Filled Nylon have been successful running in QC-10 Molds. For higher volume requirements, surface coatings are recommended. 2. QC-10 Continuous Mold Temperature should not exceed 250 F QC-10 QC-10 Yield Yield Strength vs vs. Exposure Time Yield Strength (MPa) o F (93 o C) 250 o F (121 o C) 300 o F (180 o C) 350 o F (230 o C) Exposure Time (hr) 3. QC-10 Mold surfaces can be Acid or Laser Etched for Texture 4. Shut-off angles - 5 degrees minimum is recommended, Preferred shut off angle is 7-8 degree for all matching surfaces 5. Narrow, tall standing cores should be inserted with a more stable material, P-20 MoldMAX 6. Ejection pins should be located so that they will eject even short shots. This could help eliminate mold damage that can occur when trying to remove a short shot. 7. Increase slide contact surface by 25% (un-treaded aluminum) 8. If an aluminum surface is to be treated with a hardened coating of 52RC, then the lifters and slides would not need to be oversized, the same dimensions as a conventional steel mold should be suitable. 9. The area of shut off should be typically twice the surface area of the impression, with an inch added to the W & L for each inch of depth of the impression. Example: a 6.00 x 6.00 impression = sq in x 2 = 72. The square root of 72 is 8.5, 2.00 depth of the impression add 2 inches x should be the block size.

3 10. If blind holes are created during the mold build that need to be plugged, QC-10 is recommended as the material for this plug. Using a lesser grade alloy such as 6061 can be the cause of pre mature failure. Two dissimilar metals in contact in a corrosive environment can result in galvanic corrosion. In the QC galvanic couple, QC-10 is expected to act as the anode (more active) and 6061 as the cathode (more noble). 11. Thermal Expansion should be taken into consideration when designing a QC-10 Injection Mold that may incorporate inserts, slides, lifters or mounted plates that may be made with different alloys. The Thermal Expansion differences between the different alloys could result in pre-mature failure. Coefficient of linear thermal expansion for QC-10 : 13.7 x ( ) per F Coefficient of linear thermal expansion for P20 Steel: 7.1 x ( ) per F Coefficient of linear thermal expansion Beryllium Copper: 9.7 x 10-6 ( ) per F QC-10 Expansion: for every 25 F = : 100 F expansion will be P-20 Expansion: for every 25 F = : 100 F expansion will be Beryllium Copper Expansion 25 F = : 100 F expansion will be Linear thermal expansion can be expressed as: dl = L 0 α (t 1 - t 0 ) Where: dl = change in length (inches) L 0 = initial length (inches) α = linear expansion coefficient ( in/in o F) t 0 = initial temperature ( o F) t 1 = final temperature ( o F) 12. Straight Thread O-Ring Type water fittings are recommended, less stress on threads, Stainless Steel or Aluminum fittings preferred to avoid Galvanic Corrosion Issues. 13. Water Lines should be twice the diameter of the water line from the mold surface, 1.00 minimum is recommended whenever possible. 14. The pitch (distance between cooling channel centers) should be three to five times the channel diameter.

4 15. The high thermal properties of QC-10 allow for flexibility in the placement of water lines. 16. Maintain neutral water ph levels to combat premature corrosion. Water systems must be maintained at ph levels between 6.5 and Eliminate or maintain minimum levels of dispersed rust, dissolved metals, chlorinated biocides, heavy metals, chlorides, and phosphates in water. 18. When using QC-10 as an insert in a steel mold base, clearance holes should be considered in the steel mold base for water lines into the QC-10 insert. This will allow cooling water to go directly into the QC-10 without passing thru the steel. This will help to reduce corrosion and eliminate the need for o- ring seals. Pipe Nipple Steel Mold Base QC-10 Insert Clearance Hole 19. When the need for Turbulent Flow Baffles is necessary, Plastic Flow Baffles should be considered. Dissimilar materials such as QC-10 Aluminum and Brass can be the cause of Corrosion in the future. Plastic Flow Baffles as shown in the picture do have a maximum coolant temperature of 212 F. Photo Courtesy of DME

5 20. When Cutting Slots, Notches or Insert Pockets, Please refrain from cutting Sharp Corners, Use as Large of a Radius as Allowable. Sharp Corners will create a weak point in the material, cracks begin at weak points. A 45 edge should be cut on an insert to clear the radius. 45 Chamfer on Insert Use as Large of a Radius as Allowable 21. Sharp angles must be avoided to reduce local stress concentrations that could lead to early failure of the mold. Use as Large of a Radius as Allowable, the minimum should be on the core and cavity, parting line should use radii of at least 0.40, more if possible. 22. Polishing of a QC-10 Aluminum mold is basically the same and with the same equipment as with steel molds, but can be done in less time. Mirror or optical polish surfaces can be achieved, coating these types of surfaces is recommended.

6 Mold Flow For Mold Flow simulations, the criterion for QC-10 is loaded into the Mold Flow software. Density Specific Heat 2.85 g/cm3 884 J/kg-C Thermal Conductivity 160 W/m-K Elasticity Modulus 70 MPA V 0.33 Coefficient Thermal Expansion 24.7 x 10-6 m/m/ C Processing with Corrosive materials like POM (Acetal) or PVC (Polyvinylcloride) produces considerable wear in Steel mold. However, the high corrosive resistant nature of QC-10 Mold Block will combat the corrosive nature of the resins mentioned and therefore no surface treatment is needed processing corrosive resins

7 General Machining Guidelines Traditional machining operations are easily performed on aluminum QC-10 alloys. The thermal conductivity of QC-10 assists with heat dissipation. Even though QC-10 Mold Plate has been stressed relieved, some minor degree of residual stress does remain. To minimize distortion caused by these residual stresses, the following basic machine guidelines should be followed : 1. Machine or Grind to.060 inches from each side of the plate. 2. Rough machine the plate removing the majority of the material, leaving enough material for further distortion. 3. Un-Clamp plate and let stand 8-12 hours 4. Re-clamp plate for final machining. Note : Do Not Distort the plate when re-clamping, use shims where required 5. Clean up Top and Bottom for flatness Always use a good grade of coolant with a neutral ph that is free of Chlorides Machining Process Roughing Roughing Finishing Tool Description 4 Carbide Insert Face Cutter 1 Roughing 4 Flute End Mill 2 Flute Carbide Ball-Mill MILLING SPEEDS AND FEEDS Cutting Feed Rate Depth of Speed (In / Cut (In.) (sfpm) Tooth) 5, , , Tool Size RPM IPM Cutter 5, End Mill 10, /2 Ball- Mill 10, Machining Process Single Point Turning Tool Description Single Point Carbide Insert TURNING SPEEDS AND FEEDS Cutting Feed Rate Depth of Speed (In / Tooth) Cut (In.) (sfpm) 6, Stock Size RPM IPM Dia. Rod 5, Machining Process Standard 2 Flute Drilling STANDARD DRILLING SPEEDS AND FEEDS Tool Description Cutting Speed (sfpm) Feed Rate (In / Rev) Drill Size RPM IPM Carbide Drill 2,000 2, ½ Drill 12, Machining Process Gun Drilling Tool Description Carbide Inserted Hallow Point Spade Gun Drill GUN DRILLING SPEEDS AND FEEDS Cutting Speed (sfpm) Feed Rate (In / Rev) Drill Size RPM IPM ¾ Drill 2,000 5

8 Lubricant / Coolant Direct coolant flooding at the point of cutting operation contact is recommended for optimal machining of aluminum Appropriate PH levels of lubricant/coolant are PH6.5 ~ PH8.5 (If lubricants/coolants with PH Levels greater than 8.5 or less than 6.5, black spots could form on the surface.) No corrosion on non-machined area or finishing machined area when proper PH Level are maintained The Impact of Water Acidity / Alkalinity on QC-10 Although aluminum has significant advantages when compared to other metals, it is not always completely impervious to corrosion. QC-10 develops a self-healing, stable protective oxide layer when exposed to various atmospheric conditions. This protective oxide layer can become unstable when exposed to water with extreme ph levels or high acidity. As a result, the protective layer of QC-10 can break down, and its ability to automatically renew itself may not be fast enough to prevent corrosion. This prolonged condition could result in exfoliation corrosion within cooling lines. In addition, dispersed rust, dissolved metals, high chlorinated biocides, heavy metals, chlorides, and phosphates in the water system can also corrode QC-10. To avoid the possibility of corrosion, the following actions are critical: Maintain neutral water ph levels to combat premature corrosion. Water systems should be maintained at ph levels between 6.5 and 8.5. Eliminate or maintain minimum levels of dispersed rust, dissolved metals, chlorinated biocides, heavy metals, chlorides, and phosphates in water. Neutral water ph levels are best practice to combat premature corrosion of QC-10. QC-10 Material after 48 hr test EXCO Rating EA 7075 Material after 48 hr test EXCO Rating EC - ED

9 Hot Runner Use in QC-10 Injection Molds 1. Thermal insulation of the hot runner is crucial, without this, the Hot Runner will not function properly - A hot half is ideal 2. Cooling lines should not be in close proximity to the hot runner 3. Hardened steel inserts and sleeves should be used in all hot runner contact areas for thermal isolation and to prevent damage to the aluminum block during maintenance 4. All inserts must be properly designed and engineered to support the loads of thermal expansion and preload of the hot runner components 5. Gate inserts are required for some hot runner tip designs QC-10 Mold Cleaning and Oxidation Preventative It is very important that the QC-10 mold surfaces be free of all finger prints and plastics residues, especially molds with a SPI-A1 or A 2 Finish. Any Mold Cleaners and Release Agents used on the Mold Surface need to formulated for Aluminum. It is recommended to use a dry spray oxidation preventative which does not penetrate the ejector bushings and moveable parts of the mold. It is not recommended to use rust preventative or mold cleaner spray s that have been designed for Steel Molds. These types of products generally contain trichloroethylene and ethylene chlorides that react with the aluminum alloy resulting in quantities of corrosive hydrochloric acids which lead to corrosion by degrading the natural oxide protective film.

10 QC-10 High Strength Aluminum Injection Mold Operating Tips All molds can be abused by excessive clamp pressures, high injection pressures, over packing, flashing the part, jerking the mold open and closed, lack of lubrication on the appropriate components, multiple ejection, crashing the mold closed or closing up on partially ejected parts. These types of abuse are hard on steel molds and even harder on aluminum molds. Proper processing and maintaining an injection mold will help to eliminate these situations. Always avoid hard closing (slamming) of the QC-10 mold, or any mold, clamp closing speeds should be setup for rapid closing to within.250 of mold touch with the last.250 set at a much slower rate as to not slam the mold surfaces together. Always avoid excessive clamp pressures, high injection pressures, and overpacking/flashing the mold. Always make certain the Mold Protect Feature is used and properly setup, you should be able to close up on a piece of Solder without damaging the Solder. Preventative maintenance required for a QC-10 aluminum mold should not be any more than for steel, but there are different things to look for. For example, with the rapid cycle times typically achieved by aluminum molds, more gases will be released and parting line build up may occur faster. In some cases there has been a buildup of a Gray Powder type substance on the parting lines caused by Micro-Fretting. Micro Fretting is not harmful to the mold itself but as a result, parting lines should be cleaned more often than with steel molds, all mold surfaces and vents should be cleaned once per shift. Because of this same scenario, textured aluminum mold surfaces will require more frequent cleaning than the steel mold. The 1st kind of mold maintenance you can perform is aimed at reducing in-house tool abuse. Have a clean operation using well-maintained machines and have the right tools. Pay close attention to machine parallelism and alignment as part of its maintenance activities. A modest investment into preventative maintenance now can save a lot of money later if a tool needs major repair. Recommended Tools for QC-10 High Strength Aluminum Injection Mold Parts stick at times, especially at startup, proper handling of these situations in an aluminum mold is critical. Pictured below is a variety of Plastic and Cast Aluminum tools found on the internet that could be useful with a QC-10 Aluminum Injection Mold.

11 Never use hard tools (screw drivers, hammers, punches, knives on any molding surface, parting line or shutoff surface. Always use "soft" tooling like rubber mallets, punches and pliers made from plastic, soft aluminum, copper, or brass on hand to avoid damaging the mold. If possible, check the hardness of the tools prior to using them. QC-10 hardness is HB, tools should be softer, Repair of QC-10 Aluminum Mold Surfaces Welding In the back of every molder s mind is this question; If we have a crash, can I repair this new QC-10 mold? Production environments are tough places. Today s injection molds are subject to hundreds of thousands of cycles, stuck ejector pins, and the occasional hung up part. All can lead to damage to the surface finish of an injection mold. With Alcoa s commitment to the injection mold industry, welding experts at the Alcoa Technical Center have developed weld wire for surface repairs of smooth and textured molds made from QC-10. A near perfect match of alloy allows the weld repair expert to perfectly match the material in order to achieve near perfect color match and textured characteristics. With easy training and shop floor techniques, QC-10 Weld Wire allows a manufacturer to quickly and confidently repair his QC-10 mold and get it back into production. Alcoa has demonstrated the ability to weld repair surface anomalies and wash outs of up to ½ inch in depth. It must be noted that at this time, weld techniques on any high strength aluminum alloy is not recommended for structural welds, weldment build-ups, or depths greater than ½. However, such mechanical joining techniques such as freeze-plugs are technically feasible and work very well in QC-10 tooling. Following the instructions in the Alcoa QC-10 Weld Guideline, Alcoa has demonstrated that a weld repair can be adequately employed in surface repair methods up to ½ in depth and re-machined and / or retextured in order to repair surface anomalies. Freeze Plug A viable alternative to weld repair is the use of a Freeze Plug. The use of Freeze Plugs is not possible with steel due to material phase changes at low temperatures. Advantages of a Freeze Plug: Allows exact matching between materials Can be machined to correct dimensions and finish No heat affected zone Damaged Area Machined Hole Machined Freeze Plug Finish Machine

12 Cold Spray Cold Spray Technologies is a process that was developed in the Soviet Union in the mid 80 s. A Team at the Alcoa Technical Center has been experimenting with Cold Spray Technologies for several years with success in many areas. Cold spray is a materials deposition process in which relatively small particles (ranging in size from approximately 5 to 100 micrometers (μm) in diameter) in the solid state are accelerated to high velocities (typically 300 to 1200 meters/second), and subsequently develop a coating or deposit by impacting an appropriate substrate. Various terms including kinetic energy metallization, kinetic metallization, kinetic spraying, high-velocity powder deposition, and cold gas-dynamic spray method have been used to refer to this technique. In most instances, deformable powder particles in a gas carrier are brought to high velocities through introduction into a nozzle, designed to accelerate the gas. The subsequent high-velocity impact of the particles onto the substrate disrupts the oxide films on the particle and substrate surfaces, pressing their atomic structures into intimate contact with one another under momentarily high interfacial pressures and temperatures. The Alcoa Technical Center is currently performing a number of tests to determine if Cold Spray Technology would be a viable process for the repair and / or changes to a QC-10 Injection and Blow Mold. We have seen some very promising results to date with limited run time on an injection mold, high volume injection molds will be use soon. Pictures on the next page show a sample of repairs that have been studied. Machined Simulated Repairs Edge Repair Hole Repair After Cold Spray Repair Acid Etched Texture Surface Note: The information presented in this document is presented as guidelines and does not incur the liability of Alcoa.