31May

Prototyping Strategies for Die Casting

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When it was first introduced as a production method in the mid-1800s, die casting was used almost exclusively to make type for printers. Die casting enabled manufacturers to produce the individual letters and punctuation marks printers needed for their typing machines faster while maintaining size and quality consistency. These enhanced production capabilities reduced printing errors as well as the time it took printers to set up their printing equipment, which led to unprecedented growth in the printing industry.

By the early 1890s, manufacturers began to expand their use of die casting and started to make dies that could be used in other industries to produce consumer goods as well as the parts industrialists needed to fabricate those goods. The predominant materials used by early die casters were lead and tin, but additional alloys such as copper and magnesium alloys were introduced over the ensuing decades. These available alloys meant die casting could be used to produce items with different characteristics, such as greater heat and erosion resistance, as needed.

Strategies for Die Casting Prototyping

Just as die casting has expanded into many industries and new alloys have been introduced over time, additional die casting techniques and strategies have been developed since the process was first employed to make type for the burgeoning printing industry. While a high-pressure die casting technique is typically used today, other casting methods are often used in the die cast prototyping process.

Current die casting prototyping methods include the following:

1 – Single-Cavity Prototype Die

If you’re going to conduct extensive testing, the single-cavity prototype die process is likely your best choice from among all of the current die casting prototyping strategies except for actual die casting. Arguably, the biggest advantage of this process is that it allows you to thoroughly evaluate your end product’s critical characteristics, including the finish on its exposed surface.

With approximately 75 percent of production dies requiring either minor or major changes, another benefit of the single-cavity prototype die process is that graphics2you can make certain changes to the design of your prototype’s die after the initial round of parts is produced, thus avoiding costlier changes down the line.

The original die’s insert can often be used in the final production phase as well. With the single-cavity prototype die process, it normally takes less time to create your final dies as well as your secondary trim tools compared to other die casting prototyping strategies.

Due to the cost involved and the time it sometimes takes to create dies, the single-cavity prototype die process may not be suitable if you don’t have sufficient lead time or if there are uncertainties regarding the design of your product.

2 – Gravity Casting

The gravity casting process is the most popular choice to create die cast prototypes because it is less expensive than the single-cavity prototype die strategy for small amounts of product. The gravity casting process also doesn’t require as much lead time as single-cavity prototyping does. Gravity casting includes most investment casting and plaster molding casting strategies.

While gravity casting may be more affordable, it has some drawbacks that need to be considered when you’re deciding which die casting prototyping strategy you’re going to use. Since they generally have less porosity, a gravity casting typically has greater fatigue strength than a die casting does, for instance. Die casting can produce an end product with precise dimensions, but additional machining will be required to achieve the same exacting dimensions when gravity casting is used. Gravity casting also cannot achieve the very thin wall widths that can only be produced by die casting, although the casting technique can yield walls with greater widths.

3 – Rapid Prototyping

Rapid prototyping for die casting is often associated with various processes, including stereolithography, laser sintering and fused deposition modeling. Contingent upon a prototype’s geometry, prototyping for die casting parts using one of these methods can usually yield an initial part in as little as 5-8 weeks. These prototyping strategies for die cast parts use a sterolithography model to create H-13 steel dies using pressure die casting instead of gravity fed die casting.

Since the alloys as well as the physical and thermal properties used in rapid prototyping are the same as in the production run, rapid prototyping enables you to perform a thorough and accurate analysis of your product before you invest in the construction of intricate, expensive die casting dies. For the same reason, rapid prototyping is typically your best choice if you want to produce up to several thousand units while your production dies are being fabricated.

Die casting rapid prototyping is often referred to as the “steel process.” This method is not usually appropriate for work involving thin and/or tall standing detail on parts. It’s also not the ideal choice for a project requiring cast-in water lines.

4 – Plaster Mold Prototyping

Also known as rubber plastic mold casting, or RPM, plaster mold prototyping is a gravity-based casting strategy that works with aluminum, magnesium, zinc and ZA alloys. Working with a stereolithography model, an initial prototype can be produced in just a few weeks. This technique enables you to make any necessary changes to a part’s geometry quickly and simply. With a cost that is only about 10 percent of the cost to construct a production die, plaster mold prototyping can be more economical than other strategies for die casting prototyping.

Although it can produce parts in many sizes, RPM is generally most appropriate if your part is in the range of two to 24 cubic inches. Plaster mold prototyping is capable of producing a few or up to several thousand working die cast prototypes, making it an appropriate method to use to make a prototype if the quantity of product you need is not large enough to justify the cost of hard tooling.

Plaster mold prototyping is able to replicate any castable geometry as well. While that is an obvious benefit, it can also lead to problems because it allows designers to erroneously use geometry that can drastically increase die casting costs or make a shape that is ultimately impossible to die cast.

5 – Machining From Similar Die Castings

Machining from similar die castings involves creating prototypes from existing die castings that have a size and shape similar to the prototype you want to have made. If you want multiple prototypes of small parts, it’s possible for them to be machined out of a single large die casting’s heavier areas using this strategy. Appropriate for creating small gears and screw-machined items, among other parts, machining from similar die castings is a good choice if you need a large number of prototypes and have access to the automatic machining processes and materials needed to make them.

While this approach to die casting prototyping may seem convenient, it does have drawbacks that can be significant. First, the dimensions and shape of the prototype you want to make are restricted by the size and form of the die castings that are on hand. This die casting method also removes the dense, thick skin a production die casting normally has.

In the paper, The Significance of the Die Cast Skin Pertaining to the Fatigue Properties of ADC12 Aluminum Alloy Die Castings, Briggs & Stratton reported that when their skin was machined off, the yield strength and fatigue strength of die castings made from aluminum were reduced by more than 10 percent and 39 percent, respectively.  Additionally, a study performed by the U.S. National Energy Technology Laboratory revealed that if all or a portion of the skin was removed from a zinc die casting, the casting’s yield strength dropped by almost 10 percent.

6 – Machining From Wrought or Sheet

The list of strategies for die casting prototyping includes machining from wrought or sheet when you want a prototype made from sheet or extracted aluminum and magnesium. When compared to die casting, wrought and sheet materials have higher ductility and lower compressive yield strength, however. These materials may also have an undesirable directional quality caused by the direction of the sheet or the extracted alloys used to make them.

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Picking the Best Die Cast Prototyping Process

In order to determine which die cast prototyping process is the right one for you, you must understand that the die casting technique used to make production castings is inherently different from the methods commonly used to construct prototypes. Due to this and the differences that exist between the alloys used in die casting and other casting methods, your prototype is probably going to have different characteristics than a production casting would have.

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For instance, a component made from die casting is going to have a skin that is normally around 0.5mm thick.  This skin gives die cast parts a considerable amount of their tensile strength and fatigue life. While the skin is a vital component of a die cast casting, a finished machined prototype must have had either a portion or all of its skin removed just to be created.

Given that the die casting process involves certain steps such as rapid cooling, quick solidification and high pressure on liquid metals, among other measures, die casting gives a component mechanical characteristics that a prototype made with another method might not have. Although the difference is normally negligible, the core of a die cast item may contain porosity, which might make it less dense than castings created using alternative techniques. Depending on the die casting prototyping strategy you choose, it may be able to closely replicate many of the mechanical properties associated with die cast castings.

As a general rule, the alloys that are typically used in die casting are not appropriate to use with the gravity casting prototype process or machining from wrought or sheet because their chemical makeup is different from the chemical composition of the alloys used in the prototyping techniques. The zinc alloy group used for die casting includes Zamak 3, 5 and 7, which contain four percent aluminum. Since this group is touchy when it comes to the rate of solidification and the strength and hardness of a gravity casting are measurably less than they are in die cast castings, this group of Zamak alloys should not be used in the gravity casting prototyping process.

Instead of Zamak 3, 5 and 7, ZA alloys should be used with the gravity casting prototyping technique to better replicate the mechanical properties produced by die casting. It is okay to use Zamak 3, 5 and 7 to produce the ornamental elements of your prototype, however, as long as the mechanical properties of these pieces is irrelevant to the functionality of your prototype.

Die Casting Prototyping

Until recently, die casting prototypes were widely considered impractical in most instances because of the greater costs involved with die casting and the additional lead time needed to develop the dies necessary to make the prototypes. During the past few years, though, innovations in the die casting industry have made the use of the die casting prototype process more affordable and efficient.

One notable advancement was the introduction of CNC machining. This high-speed machinery makes it possible to produce the tools needed for die casting much faster. Depending on the manufacturer, a company using this technology can produce a four-slide die in just two weeks, an achievement which used to take at least eight to ten weeks using more traditional production methods. If a client has a condensed timeline, CNC machining can be used to produce a prototype in less than two weeks, if circumstances permit.

The use of 3D design and simulation software has also had a positive effect on the die casting industry by making prototype die cast tooling more affordable. With the use of 3D CAD technology, the time necessary for die cast tooling design can be reduced from several days to a few hours. Additional software makes it possible to virtually prototype a concept and prevent models that are destined to fail as a function of their own design from proceeding to hands-on production.

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Premier Die Casting

If you’re interested in learning more about CNC machining, other recent technological advances in the die casting industry or the die casting prototyping options that are available to you, contact Premier Die Casting. Founded more than 70 years ago, our family-owned and operated business is headquartered in Avenel, NJ. We offer a full range of services, including die casting, CNC machining, metal finishing and assembly. Just as importantly, we have the demonstrated experience and expertise to handle your next project no matter how big, small, simple or complex it is.

Our goal is to act as an extension of our clients and support their projects in whatever way is necessary. Our excellent, personable customer service puts us at your fingertips whenever you have a question or concern. We will work with you to ensure your project meets or exceeds your expectations. When you work with us, we take your project as seriously as you do because we become as invested in its success as you are.

Part of our mission statement is to “strive to be a reliable and responsive supplier of cost effective and quality products to our customers.” We take our mission seriously and will do everything possible to ensure your project is successful by keeping costs as low as possible, maintaining the high quality of our products and responding to your needs as quickly as we can. Contact us today to become part of our extended family of satisfied clients.

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