DMLS 3D Printing Design Guide

This article is a DMLS 3D printing design guide which includes technical design specifications, materials, limitations and an introduction into the post-processing options available.

Introduction:

Direct Metal Laser Sintering (DMLS) is an Additive Manufacturing method that builds prototype and production metal parts using a laser to selectively fuse a fine metal powder. Traditional manufacturing techniques remove material from a piece of stock to create the desired geometry. Additive Manufacturing is capable of producing highly complex features and all-in-one assemblies that would be difficult to achieve with subtractive manufacturing techniques.

DMLS 3D Printing Design Guide - typical components of a DMLS Machine

DMLS 3D Printing Design Guide – Typical Build Process:

DMLS 3D Printing Design Guide - Typical DMLS 3D Printing Process

DMLS 3D Printing Design Guide - Typical DMLS 3D Printing Process

DMLS 3D Printing Design Guide – Uses & Advantages:

DMLS creates fully functional parts out of metals such as Cobalt Chrome, Aluminum, Stainless Steel, Tool Steel, Titanium, Inconel, and many others. The typical users of DMLS fall under these needs:

Part Complexity

A key advantage of DMLS is the ability to produce parts that cannot be made using traditional manufacturing techniques. Manufacturing with DMLS can be advantageous if engineers design parts with complex geometries, such as integrated fastening features, long and narrow channels, custom contours, and metal mesh structures. DMLS allows for production of assemblies in single part form reducing number of parts, assembly time, and opportunity for failures.

In specialized applications, the weight of the part is an important criterion of the design. Using subtractive processes for manufacturing of metal mesh or weight reduced parts will dramatically increase the manufacturing time and cost due to the amount of material removed. DMLS is an optimal process for these parts as both manufacturing time and cost are reduced as volume decreases.

DMLS 3D Printing Design Guide - Complex, multi part designDMLS 3D Printing Design Guide - simplified design

Speed

Speed is an important aspect of the design and manufacturing process. Both the quality of the product and the overall time to market are driven by the ability to produce physical models in a timely manner for fit and function tests, peer review, and market feedback.

Here, additive technologies allow for faster and more efficient concept review and prototyping. Thus, DMLS parts are commonly used during pre-launch activities for product testing, whereas the final product is made with a tool (i.e. die casting, metal injection molding, sand casting). DMLS parts are commonly used to validate designs as part of final product quality assurance as well as stand in for parts early in product life.

DMLS parts do not require tooling (e.g. molds, jigs, fixtures, gauges etc.), which reduces initial part manufacturing lead time from months to days. Thus, additive technologies such as DMLS present a tremendous value for product customization and change by offering ways to create short run, customized products without incurring expensive tooling changes.

DMLS 3D Printing Design Guide – General Tolerances:

General tolerances for DMLS parts are ±0.005 inch for the first inch and ±0.002 inch per inch thereafter (±0.2 percent), but +/-0.002 inch is achievable in some materials. If CNC tolerances are required, parts will require post-machining.

DMLS 3D Printing Design Guide – Limited Build Size:

DMLS machines come in various build platform sizes, we offer the following build envelops:

DMLS 3D Printing Design Guide - SLM 280HL PSH 100DMLS 3D Printing Design Guide - EOS Metal 3D Printer

DMLS 3D Printing Design Guide – Pre- & Post-Processing:

DMLS, being a 3D printing process, is falsely associated with the simplicity implied from other 3D printing processes. Preparation of the design before being sent to the DMLS machine and the post processing afterwards can be time consuming. All modern manufacturing processes have before and after steps. CNC, for example, requires the programming of tool paths, machine setup, cutting and grinding, then polishing and de-burring afterwards. Prior to being sent to the DMLS machine, part support structures are designed and built. This step may take up to an hour and may determine success or failure the job.

DMLS post processing consists of:

For additional information on the post processing offered by F3DP, please visit this page.

DMLS 3D Printing Design Guide - Cutting metal printed parts off a build platform with a wire EDM

Support Structures:

DMLS parts need support structures for:

Unlike other laser and powder based additive technologies, DMLS parts move around in the build envelope if not properly secured to the build platform. Movement of the part occurs from the act of spreading a new layer of powder over the previously sintered layer or larger cross sections of the metal part warping during the sintering process. Movement of the part during the build will cause failures in part accuracy and could potentially lead to machine crashes.

A further reason support structures are required is to support overhanging geometry because the spreading would move unsupported overhands. Examples of these types of geometry are horizontal surfaces, large holes in the horizontal access, angled surfaces, arches, and overhangs.

 

DMLS 3D Printing Design Guide - add side supports to tall parts

DMLS 3D Printing Design Guide - various support structures

 

 

 

 

 

 

 

DMLS 3D Printing Design Guide - Overhang geometry man require support structures to successfully build using DMLSDMLS 3D Printing Design Guide - Overhang geometry man require support structures to successfully build using DMLS

DMLS 3D Printing Design Guide – Other Factors:

Part Strength During the Build:

During the build process, parts are subjected to forces from spreading and compacting of new layers. Tall, thin parts are susceptible to these lateral forces, causing inaccuracy in the parts’ features due to improper design or lack of support structures.

DMLS 3D Printing Design Guide - example of warping on a tall, thin part without support structuresDMLS 3D Printing Design Guide - examples of potential design improvements to prevent warping

Load Bearing Features:

Load bearing part features require further guidelines for height to cross sectional ratios to ensure feature integrity. The figures at left describe feature height to wall thickness ratios of load bearing walls and pins.

DMLS 3D Printing Design Guide - load bearing walls and pins charts

 

Distance Between Features

During the DMLS process the laser creates a melt pool that is slightly wider than the laser diameter from heat dissipating into the surrounding powder. This will cause features that are close to each other to bond together or create a section of sintered powder that cannot be removed from between sintered areas in the part. Distance between features should be at least 0.4-0.5mm to adequately remove powder and allow for part movement.

DMLS 3D Printing Design Guide - features that are close together can be an issue for the DMLS process

DMLS 3D Printing Design Guide – General Design Tips:

Wall thickness – The minimum wall thickness to ensure a successful 3D print with most materials is 0.4mm. Finer structures are possible, but are dependent on material, orientation, and printer parameters.

DMLS 3D Printing Design Guide - wall thickness

Pin diameter – The minimum reliable pin diameter is 1mm. Smaller diameters are possible, but will have reduced contour sharpness

DMLS 3D Printing Design Guide - pin diameter

Hole size – Holes diameters between 0.5mm and 6mm can be printed reliably without supports. Support free building of hole diameters between 6mm and 10mm is orientation dependent. Horizontal holes with a diameter greater than 10mm require support structures.

DMLS 3D Printing Design Guide - hole size

Escape holes – Holes are required on hollowed metal parts to remove unmelted powder. A bore hole diameter of 2-5 mm is recommended. Using multiple escape holes will greatly improve the ease of powder removal.

DMLS 3D Printing Design Guide - escape holes size

Overhanging Surfaces – The minimum angle where support material is not required on an overhanging surface is 45º relative to the horizontal in most cases. It is possible to reduce this angle further by optimizing the laser parameters.

DMLS 3D Printing Design Guide - overhung surface

Unsupported Edges – The maximum length of a cantilever-style overhanging surface is 0.5 mm. An overhanging horizontal surface supported on both ends can be 1 mm long. These rules will apply to embossed and engraved features with unsupported surfaces as well.

DMLS 3D Printing Design Guide - unsupported surfaces

Aspect Ratio – The maximum ratio between the vertical print height and the part section is 8:1 to ensure stability of the printed part on the build plate.

DMLS 3D Printing Design Guide - aspect ratio

How to use this DMLS 3D Printing Design Guide to influence your designs:

The quoted price of parts is heavily influenced by factors such as support structure design and removal of support. Therefore, minimizing the amount of support structure required will decrease design time, build time and post processing required.

The best way to accomplish this is to make the geometry as self-supporting as possible:

EXAMPLE #1: In this example the flanges towards the top of the part will cause a problem. The bottom facing surface of the flange will require some form of support. Adding a chamfer or a fillet to the overhanging geometry makes it self-supporting.

DMLS 3D Printing Design Guide - part redesign example 1

EXAMPLE #2: In this example the sloping angle of geometry is changed, making it self-supporting. Note that angles from 30°- 45° will self-support with some surface roughness and angles >45° will have a smoother surface finish.

DMLS 3D Printing Design Guide - part redesign example 2

EXAMPLE #3: Reduce mass and volume by using self-supporting features in the vertical axis.

DMLS 3D Printing Design Guide - part redesign example 3

EXAMPLE #4: The price of DMLS parts is heavily influenced by build time and the amount of material being used. The surface area to volume ratio of a part plays a large role in determining the quoted price of a given part. A part with reduced mass allows for a lower price because it takes less time to build, uses less material, and has a higher success rate of being produced correctly the first time.

The volume of a part is decreased, either by redesign or by using another manufacturing process to create the geometry, the overall part price will go down significantly. In this example the important features of a mold are built using DMLS and the surrounding material is milled to save on overall assembly cost.

DMLS 3D Printing Design Guide - part redesign example 4

 

 


Have questions or want to have us look over your part and make design suggestions? Contact us:

Sales@Forerunner3d.com – 231.722.1144

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