Precision Casting

What Is Precision Casting?

Precision casting is a term which is sometimes used to describe investment casting (also known as lost wax casting). The near-net shape and complex geometry parts that can be produced from the investment casting process makes it the ideal manufacturing process for components across a wide range of industries.

Investment casting (also known as Lost Wax Casting & precision casting) is a manufacturing process that allows us to produce a replica metal casting from a wax pattern. The wax patterns for investment casting can be manufactured by traditional methods (using a wax injection mould) or by 3D printing. The Investment casting process is an method of coating the wax patterns in several coats of ceramic, before melting away the wax pattern to create a shell. This shell is then filled with molten metal to produce the new metal casting.

How long has Precision Casting been around?

The ancient process of Precision casting ( Investment or lost wax casting) has been around for over 5500 years. The process was used in Egypt and China to produce ornaments and jewellery using Beeswax to create the patterns.

Why is it called Investment Casting?

The process is called Investment casting, due to the layering of the ceramic to build the shell, which is known as ‘investing’.

precision-casting

What Components can be Manufactured using Precision Casting?

Most components can be manufactured using Precision casting and applications are limitless. The advantage of Precision casting is that you can cast in a large variety of metals and alloys. The main constraint is size which, at our UK foundry is limited to 400 x 400mm and a total poured weight of 25kg. Our overseas partners can produce castings up to one cubic metre and up to 120kg ferrous and 40kg non-ferrous metal components.

We produce investment castings for a wide range of industries, such as oil & gas, automotive, nuclear, motorsport, rail, marine, and medical just to name a few. Due to the nature of the process, we can manufacture complex parts, with less constraints eliminating the need for draft angles in the design. The ability to 3D print the wax patterns allows freedom of design and shortens the lead times.

Investment-Casting-Component

Which Metals & Alloys can be Cast using Precision Investment Casting?

A vast selection of non-ferrous & ferrous metals & super alloys.

We cast over 50 grades in various metals and alloys such as;

More information regarding the specific grades we cast can be found on the metals & alloys pages (links in the list above) or by visiting the technical data page.

Lestercast offer a variety of treatments and finishes alongside the casting facilities.

 

Surface Roughness of Various Casting Methods

A good surface finish can be achieved from investment casting. The surface finish of investment casting is typically superior to traditional sand casting, and is in fact closer to the surface finish that would be expected of die casting. Below is a guide giving the surface finishes achievable with the different casting methods;

  • Die casting – Ra value of 0.8 – 3.2 µm
  • Investment casting – Ra value of 1.6 – 6.3 µm.
  • Sand casting – Ra value of 12.5 – 25 µm
Investment-Casting-Bentley-'Flying-B'
Investment-casting-for-Automotive-industry

The Advantages of Investment Casting / Precision Casting

Due to the nature of the Precision Investment casting process, a casting can be produced with a very good surface finish, and only minimal machining required. Customers can produce near-net shape, detailed, intricate designs with little wastage. Investment Casting can be particularly advantageous when a single casting design can replace a fabricated assembly component. The misalignment that can occur during the welding of fabricated parts, along with the risk of failure of the weld, is eliminated. The investment casting process also allows thin-walled parts (typically as low as 2mm) to be manufactured.

Stainless steel investment casting

The Precision Casting Process

  1. Feasibility & Quotation

The customer sends us a request for quotation (RFQ) which normally contains drawings and/or 3D CAD files, production quantities, alloy grade, quality and NDT standards. We also require information on post-casting requirements such as heat treatments, machining, painting etc.

Initially our engineers evaluate the components feasibility for investment casting from the CAD and identify any possible manufacturing defects that could occur.

Investment casting simulation software would then be used to simulate the flow and solidification of the metal. Collating this information and applying our extensive knowledge and experience, ensures that we achieve the best results.

Once all the RFQ criteria has been reviewed, via our formal process, a quotation is generated and submitted to the customer.

Investment Casting Simulation Software
  1. Tooling

When the customer (with our guidance) has decided whether they would like to proceed with the wax injection mould tooling, the tooling is manufactured. This takes approximately 3-6 weeks. The economics of having dedicated tooling is carefully considered during the RFQ process, and options are discussed with the customer. If the customer prefers to use 3D printed wax patterns, patterns are then printed at our 3D printing facility. In many cases, in particular, where sizable quantities are required, the need for dedicated wax injection mould tooling is the best option.

Tooling For Investment Casting
  1. Wax Pattern Production & Assembly

The wax patterns are created by injection mould in the wax room, or 3D printed, and attached via a gate to a runner system (referred to as a ‘tree’). A ceramic pouring cup is attached to the tree, to form a complete assembly.

Depending on the size of the component, potentially over 100 single wax patterns can be attached to a single tree.

Wax - Investment Casting
  1. Shelling

The ‘tree’ is transferred to our shelling department where it is first degreased to remove any organics, and prepare the wax surfaces for priming.  The ‘tree’ is submerged into a water-based slurry and then immediately rotated in a rainfall sander to create the first coat and fine surface finish, and then dried. The process is repeated many times to form a thick hard coating, ultimately forming the ceramic shell.

Investment casting ceramic

 5. Autoclave

The ceramic shell is then transferred to the Autoclave, where pressurised steam melts the wax so that it drains out of the shell. The de-waxed shells are removed from the autoclave and allowed to cool.

Investment Casting - Autoclave

      6. The Pre-Heat Furnace

The pre-heat furnace provides three key functions. Firstly, the ceramic shell is fired in order to create a hard structure. Secondly, pre heating allows controlled thermal expansion of the ceramic to take place. This is necessary to reduce thermal shock when molten metal is poured into he shell. Lastly, any residual wax that remains in the shell cavity after dewax, is burnt off.

Investment Casting Furnace

          7.    The Pouring

Once pre heated to the optimum temperature the shell is taken directly from the pre-heat furnace and secured to a roll over induction furnace. The molten metal in the induction furnace, has been prepared to the correct composition and pouring temperature. Once secured, the entire induction furnace and shell are rotated under controlled conditions, thus allowing the molten metal to disperse evenly throughout the shell.

Investment casting foundry

      8. Cooling

After pouring, the shell is then transferred to a sand bed where it is left to cool until the metal temperature has fallen below its solidus temperature, and has completed all metallurgical phase changes.

Investment Casting Foundry

        9. Knockout 

Once a safe handling temperature has been reached, the shell is moved to a vibratory shake-out cabinet, where the ceramic is separated from the casting.

Knockout-machine-investment-casting

        10. Cut off

The individual investment castings are then removed from the ‘tree’ using a semi-automatic cut-off machine.

Investment Casting - Cut-off-machine

           11.   Fettling

Any excess metal is further removed via the use of precision air tools and linishing belts. The feed gates are removed by In Gating & Linishing. The castings are then subjected to a shotblast process which removes any residual ceramic and improves the surface appearance.

Fettling for Investment casting

          12.    Inspection

Every single Investment casting follows a bespoke inspection process. This can include CMM, gauging and visual criteria to ensure that the parts conform to both our Lestercast high quality standard and our customer requirements. More information on our inspection services can be found here.

Investment Casting CMM Inspection

            13.     Shipping

The precision castings are packed into our branded containers & shipped to the customer or transferred to our secure on-site stock holding facility, until the customer requests transportation.

Stock holding warehouse Lestercast

If you would like to speak to one of our engineers about our precision casting services, we would love to hear from you! We are able to offer new customers a tour around our facilities and our engineers are available to advise you on the best manufacturing processes for your project.