Reporting on the latest case studies and research results in metal 3D printer R&D

Reporting on the latest case studies and research results in metal 3D printer R&D

2nd report: In today's era, metal 3D printers will be rejected if they are not
high-precision - The struggle of overseas companies

Our hybrid laser and milling metal 3D printers (OPM method) often are compared with metal 3D printer technology from Europe and North America that uses lasers only.

As it becomes well known around the world, I think that many people understand the biggest difference between the OPM method and metal 3D printer technology from Europe and North America that uses lasers only to be the fact that the OPM method adds a milling function. But in this report I would like to describe more distinctive properties and differences from our experience as people who use them daily in practical operations.

I’ll start by giving the conclusion first: I think that in terms of precision, products output using the OPM method (such as parts and molds) can be considered something completely different from those produced using other companies’ metal 3D printers.

Metal 3D printing technology makes it possible to form complex shapes that were not possible using traditional technologies, but whether the finished products achieve the required precision of measurements and whether they can guarantee the mechanical strength and performance that their internal structures were designed to have depends on whether the processes conducted inside the equipment are conducted properly.

To begin with, please take a look at the differences in precision of preparation between European and American metal 3D printers and the OPM250/350L in Fig. 1. It shows a comparison of the base plate sets between European and American metal 3D printers and the OPM method.

Fig. 1. Differences in precision of preparation between European and American metal 3D printers and the OPM250/350L

In European and American metal 3D printers, the process begins by setting the work on the work table with at least two parallel surfaces (top and bottom). While they appear to have visible laser pointing functions, they lack functions for numerical measurement and feedback of positioning coordinates and parallelism. This is because they are not simply controlled by NC control equipment. In a sense, their base plate is treated as nothing more than a stand.

In contrast, the OPM250/350L features a laser and optical system and NC control equipment atop a sturdy, die-cast structure like machining equipment.

Looking at the process of preparation:

  • The base plate uses a six-surface milling machine (with precision control)
  • During positioning, the main axle is controlled and parallelism is measured using a dial gauge.
  • The main axle is equipped with a point finder to measure positioning.
  • The completed object too is measured using the point finder, to check whether the required precision has been achieved.

The high-precision laser and milling processes start when the base plate is positioned.

I’m sure this is clear by now, but the concept of this method is completely different from the preparations stage.

Personally, I see European and American metal 3D printers (M3DP) truly as printers, with a mechanical structure based on lasers and optics. Their equipment frames too use welded chassis.

I think that the OPM250/350L should be referred to as metal 3D machining (M3DM), since it adds laser and optics to a machine tool, with the stress on precision. Since I doubt that manufacturers will accept parts that do not deliver assured precision, I believe that the OPM method has the best chances of being adopted as metal 3DP technology that will become deeply rooted in manufacturing.

Next, there are three patterns to the molding/mechanical parts processing methods output from the OPM method.

A look at Fig. 2, OPM Choices of Processing Methods,shows that these are the following patterns:

・Type A Repeated laser process and milling inside the equipment to process molds/parts with an all-milled surface
・Type B Near-net shape produced using a laser, and the milling function inside the equipment is used from above to process the mold/part in one process (limited to objects within the range reachable by the effective length of the tool)
・Type C Near-net shape materials produced using laser, and then transferred to another standard machine tool to add the datum surface (milled surface)

The optimal pattern may be chosen based on consideration of matters such as the user’s purpose of use, delivery time, and cost.

Comparison based on the exact same shape shows that in terms of both cost and delivery time these patterns can be ranked as follows: Type C < Type B < Type A. However, the most important topic for us is the fact that Type A (all-milled) under the OPM method has accelerated R&D with the goal of surpassing traditional methods in terms of both cost and delivery time.

We have realized these research results with the products exhibited at JIMTOF2016. I hope you will come and take a look at them.

Fig. 2. OPM choices of processing methods

Returning to an earlier subject, at present we receive orders one after the other for processing of molds and parts from around the world. We conduct secondary processing in-house for molds and parts completed using the OPM250/350L, and we consider shipping final products that meet our customers’ precision requirements to be an important responsibility.

When we are unable to handle secondary processing in house, we ask partner companies to conduct it. Secondary processors will refuse to accept objects that lack measurement data or data for starting processing. This is because working on such objects is a gamble with a high risk of errors in processing. For this reason, the minimal requirements of such a request are an object like that under Type C plus a datum (milling) surface.

Now please take a look at Fig. 3 and Fig. 4, the Importance of the Datum Surface for Precision (i) and (ii).

Fig. 3. The importance of the datum surface for precision ①

Even if the six surfaces of the base plate have been finished in a milling machine,
the object sintered by the laser will not necessarily be in the center of the plate.
This is because the laser scanning position reflected from the galvano mirror
has deviation and accurate central coordinates cannot be measured from the plate surface. This is why it is necessary to create a measurement datum surface by milling from the side of the object.

Fig. 4. The importance of the datum surface for precision ②

There are multiple ways to create a datum surface.
Two typical patterns (shown above) are:
 ・ Finishing on the product surface using a milling feature (Image 1)
 ・ Finishing on the object plate side surface (Image 2)
We use the appropriate method in light of the conditions of each case.
The most important requirement is to finish the datum surface before removing the object from the machine.
European and American metal 3D printers are unable to create datum surfaces because they lack milling functions.
Surely anybody can see that this makes it difficult to use them to produce high-precision parts.

While it is possible to finish simple shapes such as a cylinder, a cube, or a circular cone in secondary processing at considerable cost, it takes just about as long as it would to produce them from a solid object. It is outrageous that there is no way to guarantee positioning of carefully designed internal structures such as conformal cooling channels.

For us, who carry out practical operations while negotiating with our customers on easing tolerances for measurement precision that are no less than +/-2 - 3/100 and could be as high as 1/1000, European and American metal 3DP, which is unable to create a datum (milling) surface in an object like under Type C, is not suited to manufacturing industries, which demand precision (with the exception of some large companies). It is better suited to the design and art fields and to medical fields such as dental implants and false teeth. I say every day that it would be better not to make the wrong choice. With regard to this subject, we have strong recognition among our customers and a fairly high penetration in manufacturing, and I think that this is a painful matter that must be pointed out to the leading metal 3DP firms around the world. However, I always call for using the right materials in the right place, and it is my hope that the technologies of metal 3DP will advance through a spirit of coexistence and co-prosperity. Of course, I always add that this depends on customers’ purposes of use.