Diecasting Company - South Yorkshire England UK
PMS Diecasting is very efficient and productive zinc diecasting company based in Rotherham, South Yorkshire. We have the ability to manufacture low cost or cheap diecastings for use in the global markplace. We can compete with Chinese diecastings because of the set up of our Company. We use highly productive Frech Diecasting machines and robotics to reduce labour to an absolute minimum and work a 24 hour shift pattern to ensure overhead rates are as low as possible. To ensure casting quality on high volume production we are developing 100% in-line quality checking with the use of electronic scales accurate to 1/100th of a gramme to pass and reject any castings which fall outside pre-set tolerances.
As the Company develops we will be positioned to supply high volume castings which have been 100% quality checked. This will set PMS Diecasting apart from any other diecaster in the UK or China for low cost / cheap diecastings which can be guaranteed for casting integrity and dimensional accuracy.
Zinc Prototypes
Prototypes can be quickly and economically produced using a Thermojet Printer. The Thermojet is a three dimensional wax printer which builds your part to an accuracy of 0.1mm straight from a 3D model, normally supplied as an iges file. Once your part has been made (printed) in wax it can then be coated with a ceramic shell which withstands very high temperatures. This is the basis of the lost wax investment casting process but the wax part is printed rather than cast. The wax part is melted out of the ceramic shell and then molted zinc can be poured into the cast, under vacuum conditions, to ensure all areas of the product are perfectly formed. The shell is then removed and you are left with a zinc diecasting which only requires the feed area machined off. The cost of prototyping is about £120 - £140 per part of about 30mm x 80mm x 4mm in size. Virtually any complexity can be accomodated with this process. Lead time 1 week from receipt of 3D model and order.
Benefits of Rapid Prototyping
The main benefit of prototyping is design verification, providing the opportunity to identify design flaws before a product goes into production. The further along the developmental cycle design errors are discovered, the greater the cost to fix them.
The cost of discovering design errors after the diecast tooling is complete can be even worse. The most obvious cost is tool rework. Seventy-five per cent of production dies require rework ranging from simple modifications to a major overhaul - a figure that is unacceptably high. Additional costs can include shorter tool life and late delivery of the product to the marketplace. At a minimum, a three-month delay in introducing the product to market means a loss of sales and a potential loss of market share that may be hard to recover. Appropriate use of today’s prototyping technologies can help manufacturers avoid these needless added costs and uncomfortable situations.
There are many methods of prototyping diecast parts, but two of the most effective are plaster mold casting (also known as rubber plaster mold casting - or RPM) and rapid diecasting from cast H13 steel dies (also known as the Steele process). These two techniques play different roles.
Plaster mold provides initial prototype aluminum or zinc castings in a few weeks when starting with a Stereolithography (SLA) model. This low-cost ‘soft’ tooling approach usually costs about 10 per cent of production die cost. It allows for quick and easy modifications to part geometry. That ease of geometry modification facilitates design refinement. If required, the process is capable of manufacturing thousands of parts through the use of reusable silicon rubber foundry tooling.
Rapid diecasting provides initial sample parts in five to eight weeks, depending on part geometry. The process starts with a SLA model and the casting of H-13 steel dies. This means prototypes are processed as a pressure diecasting instead of a gravity-poured casting. Alloys, physical, and thermal properties will be the same as in the production run, while RPM uses slightly different alloys with different properties. Rapid diecasting is the best method for providing short runs (up to several thousand) to enable production while final production dies are finished and qualified.
RPM and rapid diecasting can be complimentary in many cases. RPM can provide initial samples in a shortened time frame while the part design is perfected. Cast dies can offer cost savings and increased production rates before full production tooling is completed.
Plaster Mould Casting
Plaster mold casting is a quick and relatively inexpensive way of producing aluminum and zinc castings. SLA or other rapid models can be used as master models to develop tooling. The plaster process differs from the use of Quickcast™ (in which models are destroyed making each casting) in that plaster mold casting creates foundry tooling from the SLA model. Once the rubber tooling has been generated, it can be used to produce up to a thousand aluminum or zinc castings before tooling maintenance is required. Rubber foundry tooling may be cost justified over Quickcast even if only a few Quickcast models are required, depending on part complexity. For smaller quantities (less than five pieces), plaster molds can be made directly from many types of rapid prototyping models for geometries with or without side pulls. This approach is referred to as loose pattern molding. The plaster process has some invaluable properties, among them its ability to produce complex, thin-walled castings with excellent surface finishes. That makes it the ideal choice for reproducing the fine and complex details often found in SLA models. Casting lead times vary from a few days to several weeks depending on part complexity. It can cast a wide range of sizes but is most applicable to parts that fit within a 50mm - 250mm cube range. Quantities ranging from two or three pieces to several thousand pieces can be produced as functional diecast prototypes. Therefore, plaster serves as a bridge process while awaiting delivery of production tooling and, in many cases, as a production process where quantity requirements do not justify the expense of hard tooling. Ideally, the production diecaster and the plaster mold source should work closely with the end user to ensure a smooth transition between processes. Plaster mold casting can simulate any diecastable geometry and it is critical that designers do not configure the RPM casting to a geometry that will increase diecasting prices - or worse still, result in a shape that cannot be diecast.
The Process
The first step in the RPM process is to create a master model. Usually it is SLA but in many cases traditional pattern making models are still used. The parting lines are then established and negative molds are developed from the model. A silicon rubber positive is made from each of the negative molds. Gating runner systems are added as required. Next, a liquid plaster slurry is poured over the silicon rubber patterns. Once the plaster molds have set, they are removed from the rubber patterns and baked to remove moisture.
Subsequently, molten zinc is poured into the assembled laster mold. Once the metal has solidified, the plaster mold is destroyed so the part can be taken out. The reusable rubber tooling can make hundreds of molds. After the casting has passed initial inspection, gates and flash are removed and the part is now ready for secondary operations such as machining, assembly, chemical or paint finishes. Again, for time savings in creating a few pieces, plaster molds can be made directly from the SLA pattern once parting lines have been created.
RAPID Diecasting
Rapid diecasting from cast tooling is an approach to diecast prototyping and short runs that has been around for several decades, but the advent of CAD and SLA modeling is driving a renewed interest into its application. Starting with a SLA model, H-13 steel dies are cast to a net shape in a fraction of the time required for cutting tool steel. Additional geometry can be added via secondary machining. The key benefit is that prototype parts are processed as a diecasting and therefore physical and thermal transfer properties that will be identical to the production art. Additionally, this process can provide considerable cost advantage over RPM for quantities over a thousand. Since the components are run in a diecast press, large numbers of parts an be manufactured in a short amount of time
This highly accurate process is capable of casting fine detail with excellent surfaces. Complex parting lines can be accommodated, as well as side actions via hand loads. This approach is not recommended for use with thin, tall standing part detail or with cast-in water lines. Typical lead times range from five to eight weeks dependent on part size and complexity.
In the cast H13 steel die process, an initial pattern is generated via SLA or CNC with shrinkage factors scaled in. Parting lines are developed and a soft durometer negative is created in the shape of the tool. A ceramic tool is made and the steel is poured. Cavity detail can be finished if required via CNC or EDM. The inserts are squared and fitted into a standard mold base where ejection pins are added. Gates and overflows are machined in and the cast die is ready to run in a standard diecast press. Parts can be run in any diecast alloy and finishing requires only a trim and any secondary machining that may be necessary.
Enhance Competitiveness
To remain competitive in today’s markets, manufacturers are constantly searching for new benefits from prototyping that go far beyond the ability to assess the visual qualities of a design. Today, prototyping can enable actual functional, assembly and performance testing. Functional prototypes support more detailed market research to assess the viability of a product before a decision is taken to move to full scale production. All of this is made possible by prototypes that have the same or similar properties and materials as those of the production parts. As we have seen, two time-tested metal casting processes in combination with such new technologies as RP provide these benefits while accommodating today’s time-compressed engineering requirements. The ability to use rapid prototypes as master patterns in both processes provides significant time and cost savings.
Glossary of Die Casting Terms
Automation - Industry term commonly used to describe the mechanisation of various aspects of die casting process.
Blister - A surface bubble caused by gas expansion (usually from heating) which was trapped within the die casting or beneath the plating.
Blow holes - Voids or pores which may occur due to entrapped gas or shrinkage during solidification, usually evident in heavy sections. (See porosity)
Cavity - The recess or impressions in a die casting die in which the casting is formed.
Cold chamber machine - A type of die casting machine in which the metal injection mechanism is not submerged in molten metal.
Die lubricant - Liquid formulations applied to the die to facilitate casting release and prevent soldering.
Dimensional stability - Ability of a component to retain it’s shape and size over a long period of service.
Draft - The taper given to walls, cores and other parts of the die cavity to permit easy ejection of the casting.
Ejector marks - Marks left on castings by ejector pins.
Ejector pins - A rod which forces the casting out of the die cavity and off cores.
Ejector plate - A plate to which ejector pins are attached and which actuates them.
Fillet - Curved junction of two surfaces, e.g., walls which would meet a sharp angle.
Flash - A thin web or fin of metal on a casting which occurs on die partings, vents and around moveable cores. This excess metal is due to working and operating clearances in a die.
Gate - Passage for molten metal which connects runner with die cavity. Also, the entire ejected content of a die, including castings, gates, runners sprue (or biscuit) and flash.
Hot chamber machine - Die casting machines which have the plunger, gooseneck (metal pressure chamber) immersed in molten metal in the holding furnace.
Impact strength - Ability to resist shock, as measured by a suitable testing machine.
Ingot - Metal or alloy cast in a convenient shape for storage shipping or remelting.
Injection - The processes of forcing molten metal into a die.
Insert - A piece of material, usually metal, which is placed in a die before each shot. When molten metal is cast around it, it becomes an integral part of the die casting.
Loose piece, knockout - A type of core (which forms undercuts) which is positioned in, but not fastened to a die. It is so arranged as to be ejected with the casting and from which it is removed. It is repeated for the same purpose.
Metal saver - Core used primarily to reduce amount of metal in a casting and to avoid sections of excessive thickness.
Multiple cavity die - A die having more than one duplicate impression.
Overflow - A recess in a die connected to die cavity by a gate to assist in proper venting.
Parting line - A mark left on die casting where the die halves meet; also, the mating surface of the cover and ejector portions of the die.
Plunger - Ram or piston which forces molten metal into a die.
Porosity - Voids or pores resulting from trapped gas, or shrinkage during solidification.
Process control - Where parameters of a process are studied and correctly applied in the manufacturing process to produce high quality parts.
Runner - Die passage connecting sprue or plunger holes of a die to the gate where molten metal enters the cavity or cavities.
Shot - The segment of the casting cycle in which molten metal is forced into the die.
Shrinkage, solidification - Dimensional reduction that accompanies the freezing (solidification) of metal, passing from the molten to the solid state.
Shrink mark - A surface depression which sometimes occurs next to a heavy section that cools more slowly than adjacent areas.
Slide - The portion of a diecast die arranged to move parallel to die parting. The inner and end forms a part of the die cavity wall that involves one or more undercuts and sometimes includes a core or cores.
Soldering - Adherence of molten metal to portion of the die.
Trim die - A diefor shearing or shaving flash from a die casting.
Unit die - A die interchangeable with others in a common holder.
Undercut - Recess in the side wall or cored hole of a casting disposed so that a slide or special form of core (such as a knockout) is required to permit ejection of the casting from the die.
Vent - Narrow passage at the die parting which permits air to escape from the die cavity as it is filled with molten metal.
Void - A large pore or hole within the wall of a casting usually caused by entrapped gas. A blow hole.
Waterchannel - A tube or passage though which water is circulated to cool a casting die.
For more information regarding quality checking contact Gordon Panter.
