Reproducing an Aluminum Part Without Documentation: From 3D Scan to Finished Casting

An aluminum part can be reproduced without a drawing: the original is 3D scanned, a CAD model is created from the scan, and from that come the casting pattern, the casting and the machining of functional surfaces. This solution is for maintenance departments, service shops and owners of older machines when the part cannot be purchased and repair is not an option.

In brief

• All you need for reproduction is the original, even if it is worn or cracked; ideally, all fragments should be preserved.
• A 3D model of the finished part is not yet a casting model: machining allowances, draft angles and shrinkage must be added.
• For one or a few pieces, a sand mold is usually chosen; the academic textbook "Odlewnictwo" (WNT) considers it economical for any batch size.
• A copy of a die casting made in a sand mold often requires thicker walls: the minimum here is 3–6 mm, not 0.7–1.5 mm as in die casting.
• The alloy is determined by analyzing the chemical composition of the original or selected to suit the function of the part.

When Reproduction Makes Sense and When It Is Better to Repair or Buy the Part

Making a part from the original pays off when it cannot be purchased or the wait is too long. Before you order a scan, compare three options.

Situation	Usually the best option
Machine discontinued, manufacturer no longer exists or does not supply parts	reproduction from the original
A single crack in an easily weldable alloy, lightly loaded part	weld repair
Part available from the manufacturer at an acceptable lead time and price	purchase of the original
You need a few pieces now and more in the future	reproduction – the pattern and documentation are kept for subsequent orders
Part keeps cracking in the same place	reproduction with a design correction

Cracking in the same place is usually a design problem, not chance: a sharp change in wall thickness, a missing fillet, or a massive hot spot. When a part is reproduced, this can be corrected, because a new model has to be made anyway. We cover when weld repair of a crack makes sense and when it does not in a separate article.

Reproducing a Part Step by Step

1. Assessment of the original. A process engineer checks whether the part is complete, how worn it is, and which process it was made with. This determines whether a scan is enough or missing sections have to be reconstructed.
2. Gathering requirements. Part function, loads, operating temperature, media contact, leak tightness, fits with mating parts, and quantity.
3. 3D scanning and measurements. The scanner captures the surface of the part. Fitted bores, threads, and datum surfaces are additionally measured with contact instruments.
4. CAD model. The scan is used to build a solid model that restores the designer's intent: axes, planes, and radii, with wear compensated for.
5. Alloy selection. Based on an analysis of the original's composition or on functional requirements.
6. Process selection. Depending on quantity, size, and required accuracy: sand mold, permanent mold, or, for large series, a die casting die.
7. Casting design and foundry pattern. Machining allowances, draft, shrinkage, and core prints are added to the part model, and then the pattern is made, for example from wood, plastic, 3D printing, or aluminum.
8. Casting and machining. After pouring and cleaning, the functional surfaces are CNC machined.
9. Inspection and documentation. Measurement, a trial assembly with the mating part and, if agreed in the order, handover of the model and drawing so that the next order does not require rescanning.

A 3D scan is only the beginning: what has to be done with the model

The result of scanning is a mesh describing the surface, usually saved in STL format. This format is used for 3D printing and rapid prototyping, but design and machining require a solid model, most often delivered as STEP.

Going from a scan to a CAD model (reverse engineering) is engineering work, not file conversion. The scan shows the part as it is today: with worn surfaces, distortion, and traces of corrosion. The engineer reconstructs the nominal dimensions, straightens the planes, sets the bore axes, and selects fits for the mating parts. Missing sections are completed from symmetry or from the geometry of the components the part connects to.

The second step is converting the model of the finished part into a model of the raw casting. The following are added:

• machining allowances on surfaces that will be machined – their size follows from dimensional tolerances and machining allowances for castings,
• draft angles in the direction the pattern is withdrawn from the mold,
• casting shrinkage – the pattern is larger than the casting by a value selected for the alloy and the molding method,
• core prints for holes and passages that cannot be formed directly in the mold,
• fillets and gradual changes in wall thicknessthat reduce cracking.

Shrinkage is selected by the process engineer. The pattern must even account for the molding method: with machine compaction of the sand under high pressure, the assumed linear shrinkage is reduced by approx. 30%, because the sand springs back once the pressure is removed (p. 280). A pattern for hand molding and a pattern for an automatic line are therefore not interchangeable.

Which alloy? Analysis of the original and old designations

The most reliable way is to analyze the chemical composition of the original with a spectrometer. This is the same type of instrument that foundries use to monitor the composition of their melts on an ongoing basis. The test usually requires preparing a small, flat spot on the part, so it is worth deciding in advance where this can be done.

The result is compared with grades according to PN-EN 1706. Old drawings and nameplates often show former Polish designations, e.g. AK7, AK9, or AK11, where the number after the letters AK indicates the average silicon content (p. 147). We explain how to translate them into current grades in our article on the old AK symbols and their EN AC equivalents.

When analysis is not possible, the alloy is selected according to the function of the part: required strength, operation in a corrosive environment, leak tightness, subsequent machining, and coating. The same alloy also has different properties in different casting processes. For example, for AlSi9Mg the minimum tensile strength is higher in permanent mold casting and die casting than in sand casting.

Identify the Original Technology Before Choosing the Technology for the Copy

Marks on a part indicate how it was made. Round ejector pin marks point to a metal mold, i.e. a permanent mold or a die casting die. Very thin walls and a smooth surface usually mean a die casting. A grainy surface and thicker walls suggest a sand casting.

The copy does not have to be made with the same process as the original, but the options then change:

Parameter (aluminum alloys)	Sand mold	Permanent mold	Die casting
Minimum wall thickness	3–6 mm	2,5–5 mm	0,7–1,5 mm
As-cast surface roughness Ra	4–10 µm	4–6 µm	0.8–1.6 µm
Economical batch size	any	from approx. 400 pcs (simple castings), from approx. 1,000 pcs (complex)	from approx. 2,500 pcs

Source: the handbook "Odlewnictwo" (WNT), tables 3.20, 3.22 and 3.23. Approximate values, dependent on the size and shape of the part.

Conclusion for single pieces: a copy of a die casting is usually made as a sand casting, so walls that are too thin have to be thickened and smooth functional surfaces machined. Thickening changes the weight and sometimes the space needed for installation, so it is checked in the CAD model before the casting pattern is made. The alloy often changes as well: grades for die casting are selected for that process, while for a sand mold an alloy with good sand casting properties is chosen, sometimes with heat treatment.

Casting pattern, casting and finishing

For one or a few pieces, the pattern cost is spread over a very small batch, so the simplest construction that will last for the required number of molds is chosen. Tooling is made once and serves the entire production of a given casting, while the other operations are repeated for every casting (p. 106). Permanent patterns are made of wood, metal or plastics (pp. 111–112); today they are often 3D printed or milled from pattern boards. We describe the materials, durability and ownership of patterns in our article on casting patterns and other tooling.

Single castings are usually molded by hand, and hand molding is less accurate than machine molding (table 5.2). For castings made of non-ferrous alloys in clay-bonded sand molds, the handbook gives a general tolerance of ±0.8 mm for dimensions up to 150 mm (table 3.21), without distinguishing the molding method. That is why fits, bearing seats, sealing surfaces and threads are designed with a machining allowance and finished on 3-axis and 5-axis CNC machines.

The last stage is inspection: measuring critical dimensions and a trial fit with the mating part. If the part works under media pressure, it is worth adding a leak test to the order.

What to Prepare Before You Send an Inquiry

The more information you provide at the start, the fewer follow-up questions and the faster the quote. Prepare:

• photos of the part from several sides, with a tape measure in the frame, and photos of the installation location,
• the original or all of its fragments and, if possible, the mating parts,
• a description of the function and operating conditions: loads, temperature, medium, required tightness,
• a list of mating surfaces and dimensions that must be kept,
• the number of pieces now and for future orders,
• any known markings: catalog number, alloy from the nameplate or an old drawing.

You will find the full list of data that is useful for every order in our article on what to prepare for a request for quotation. We explain how an order schedule works in our article on what determines the lead time of a casting.

The Right to Reproduce a Part

The part may be protected by industrial property rights, for example as a registered industrial design or a patented solution. Before ordering a copy, make sure you are allowed to make it, especially if the parts are to be sold. If in doubt, it is worth clarifying this with the rights holder or a patent attorney before placing the order.

Frequently asked questions

We will reproduce a part from the original

The foundry's family tradition dates back to 1950 and began with foundry pattern making. Today our foundry in Poznań combines 3D scanning and casting pattern preparation with aluminum casting and CNC machining. Send photos of your part for a quote and describe what it is used for – we will tell you whether it is better to reproduce it, repair it or make it differently.

Sources and standards

• M. Perzyk (ed.), Casting, WNT, Warsaw – ch. 2.1 (p. 106), 2.2 (types of patterns), 3.1 (aluminum alloys, table 3.8), 3.2 (design-for-casting rules, table 3.12), 3.3 (tables 3.20–3.23), 4.2.6 (chemical composition analysis), 5.2–5.3 (sand compaction and molding, table 5.2).
• PN-EN 1706:2020+A1:2021 – Aluminum and aluminum alloys – Castings – Chemical composition and mechanical properties