Knowledge base Applications

Producing low-cost cast metal parts using 3D Printing

Written by
Ben Redwood
Learn how castable FDM prints can be used to produce low-cost metal parts via investment casting.

Introduction

Castable FDM patterns, when used in conjunction with the investment casting process, can be used to produce large metal parts at very low cost, with features that would not be possible using traditional manufacturing techniques.

This article explains the benefits of using FDM 3D printed patterns and provides a framework for decision making on when to use this process over alternative methods, like DMLS, or CNC.

Low-cost Metal Parts is a new offering on 3D Hubs and not yet available through our self-service checkout. You can reach out directly to us to learn more about producing low-cost metal parts and to get a quote.

Metal part manufacturing

For low volume production of metal parts investment casting, CNC machining and DMLS are all viable solutions. The advantages of each method of manufacturing are summarised and compared below. More details on each method can be found further down in this article. It’s important to note that everything is ultimately dependent on the geometry of the design and the table does not always apply. It’s intended as a general guideline for decision making.

Method of Manufacturing Pattern Making Technique Pattern Format
CNC
  • Fast turn-around time
  • High dimensional accuracy
  • ~ Low cost only for small / medium sized parts
  • Design limitations
Investment casting
  • Low cost
  • Highly complex geometries (non-machinable designs)
  • ~ Moderate turn-around time
  • ~ Good dimensional accuracy
CNC CNC metal die (> 50 parts)
  • All sizes
  • High feature detail
  • High cost (die)
CNC pattern (wax) (< 50 parts)
  • All sizes
  • High feature detail
  • ~ Low / moderate cost
3D Printing SLA / DLP pattern (wax / plastic) (< 50 parts)
  • Low cost
  • Extreme feature detail
  • Only low cost for small parts
FDM pattern (plastic) (< 50 parts)
  • Lowest cost
  • ~ Moderate feature detail
  • Design limitations
DMLS
  • High dimensional accuracy
  • High complex geometries (non-machinable designs)
  • ~ Moderate turn-around time
  • High cost

A cost comparison of each of the technologies shown above is illustrated in the table below. 3 different parts were compared, each with varying geometries. All quotes are for parts made from stainless steel. All parts are approximately 150mm x 130mm x 55mm in size.


CNC DMLS Investment casting (3D printed pattern)
Number of parts 1 5 25 1 5 25 1 5 25
$2,705

LT: 3 days
$11,610

LT: 5 days
$51,350

LT: 7 days
$1,990

LT: 7 days
$9,200

LT: 7 days
$45,800

LT: 14 days
$105

LT: 14 days
$480

LT: 14 days
$2260

LT: 21 days
$730

LT: 3 days
$3,400

LT: 4 days
$16,100

LT: 10 days
$2,555

LT: 7 days
$12,115

LT: 14 days
$59,925

LT: 14 days
$140

LT: 14 days
$632

LT: 14 days
$3100

LT: 21 days
$660

LT: 3 days
$3,000

LT: 4 days
$14,300

LT: 10 days
$1,760

LT: 7 days
$8,130

LT: 14 days
$39,980

LT: 14 days
$160

LT: 14 days
$720

LT: 14 days
$3390

LT: 21 days

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Using 3D printing to produce metal parts

DMLS

DMLS is a powder bed fusion technology that is used to produce metal parts to a high level of dimensional accuracy. The additive nature of 3D printing means that very complex designs are able to be created. The design freedom offered by DMLS has seen it adopted by many industries (automotive and aerospace) where weight optimisation and performance are critical (the cost of operating a commercial aircraft is roughly €1000/kg meaning any weight saving result in significant savings in operation costs). This has seen these industries willing to justify the high per part cost of DMLS based on the cost savings of producing complex lighter parts.

DMLS can produce parts from a large range of metals including aluminium and stainless steel as well as exotic biocompatible materials used in dentistry and medical industries like titanium. The main limitations of DMLS are the high cost, small build size and long lead times compared to other 3D printing technologies. Parts also require support material to limit the likelihood of distortion and warping occurring and this must also be removed after printing further increasing lead time and cost.

A large number of metal crown and bridge copings printed in a single print (image courtesy of Renishaw)

Investment casting

The investment casting process traditionally uses wax patterns to produce molds for casting, as it has a very clean burn-out with no residues. The image below presents the process.

For low-run investment casting, patterns are traditionally machined from a wax block via CNC. Alternatively, for larger series, a die is machined and the patterns are created by casting the wax using the die. Tooling is a very expensive investment with production of the dies often taking a very long time (2 - 6 weeks).

3D printing is now regularly used in conjunction with a range of investment casting applications to produce patterns from castable materials. Castable 3D prints are commonplace in the dental and jewelry industries and are generally produced via the SLA / DLP printing process. This is a vat-photopolymerization technology that is able to produce parts with a very smooth surface and extremely fine details. The main limitation around SLA is the printer build volume size, or the high cost involved for larger patterns. For larger metal parts, castable FDM offers a cost effective, rapid solution.

Small, intricates design are perfect for SLA investment casting. The image above shows a castable pattern (left) printed via the SLA process and the final cast ring (ring) (image courtesy of Formlabs).

For larger metal parts, castable FDM offers a cost effective, rapid solution.

Castable FDM

For larger parts, creating patterns via SLA no longer becomes feasible due to the high cost of resin and the build volume of most SLA machines. Castable FDM offers a low-cost solution allowing parts to rapidly be printed. FDM is a material extrusion technology. After printing, the surface of the parts are smoothed via micro-droplet polishing resulting in patterns with very smooths surfaces (a requirement for a high quality investment cast).

A range of FDM printed patterns, molds and final cast parts.

There are several advantages to using FDM to produce investment casting patterns. These include:

  • Low-cost: FDM is the lowest cost method of 3D printing and eliminates the need for expensive tooling.
  • Large build size: FDM printers typically have a much larger build size (up to 450 x 450 x 650 mm) when compared to DMLS or SLA printers. As material costs are low, FDM is particularly more competitive as part sizes increase.

The process from 3D printed pattern to metal part

Written by
Ben's picture
Ben Redwood

Mechanical engineer working at 3D Hubs

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