Laser Weld Strength - Laser Welding Medical Instruments

[b9ofus]

We are laser welding medical instruments togeter and need to do a strength test. Two pieces we are currently needing to test are Ø11.00 mm OD and Ø9.00 mm ID. The will be welded completely around the OD. The joint will be a lap joint. Weld depth will be approx .2mm. Is there any kind of spec for what the weld strength should be on medical instruments?
Thanks for your help.

[Ronen E]

In Reply to Parent Post by b9ofus

We are laser welding medical instruments togeter and need to do a strength test. Two pieces we are currently needing to test are Ø11.00 mm OD and Ø9.00 mm ID. The will be welded completely around the OD. The joint will be a lap joint. Weld depth will be approx .2mm. Is there any kind of spec for what the weld strength should be on medical instruments?
Thanks for your help.

Hi,

Sorry, but I am not aware of any such standard (which of course doesn't mean no such standard exists). Anyway, from a performance perspective - will this joint be subject to any mechanical load? If so, IMO that should direct you to the strength requirement and test method.

Cheers,
Ronen.

[tonefordays]

In Reply to Parent Post by b9ofus

We are laser welding medical instruments togeter and need to do a strength test. Two pieces we are currently needing to test are Ø11.00 mm OD and Ø9.00 mm ID. The will be welded completely around the OD. The joint will be a lap joint. Weld depth will be approx .2mm. Is there any kind of spec for what the weld strength should be on medical instruments?
Thanks for your help.

Are there any customer requirements? Are there any welding symbols or notes shown on the drawing for the part in question?



Weld strength is going to be determined by weld size, base material, and filler metal (among others variables). I would assume that since this is for medical use, that there is a welding procedure specification that is being followed and has been approved by the customer. The welding procedure will define the limitations for the variables allowed for the given process being used. Having a qualified procedure will ensure (if followed properly) that the strength is satisfactory based on the testing involved in qualifying the procedure.

If there is a specific weld strength needed, the engineer of the parts should specify on the drawing all the requirements. Determining weld strength isn't the suppliers responsibility unless you are in control of design.

What material are you welding?

[b9ofus]

This particular customer has not approved a welding procedure. We are quite sure that the weld is strong but how strong we don't know and what strength is "Good" we don't know. There is no requirement on the drawing. Even the method of welding is up to us (Tig or Laser) The material is 17-4 SS for both parts being welded.

[b9ofus]

The part is used as some kind of angled driver. There will be some stress but I do not know to what extent.

[pkost]

I'm unaware of any general "welding in medical devices standard". There may be a device specific standard but I don't know what device you are making, even then in orthopaedics there are a number of standards that tell you how to measure the strength of a device but not what would be an acceptable limit as this is heavily dependent on application

You really need to speak to them so that you can get more detail - as I'm sure you are aware the welding process needs to be validated. Therefore the manufacturer/customer must have defined acceptable values.

[tonefordays]

b9ofus

If the customer hasn't provided any requirements, and this is a non critical device for non critical application, then as long as you follow good practice, and are aware of visual inspection criteria, all should be good.

If this is going to be an autogenous weld (no filler metal), look closely for crater cracks, throat cracks.

If you are going to use filler, be sure to use the proper filler, I believe E630 is the proper filler for 17-4, assuming the 17-4 has not been heat treated yet.

Look for discontinuities or defects such as undercut, underfill, overlap, any cracks. Cracks are never allowed regardless of size. Be sure weld profile is correct without excessive concavity or convexity.

Excessive concavity will result in a weaker weld, allowing for the possibility of cracking with repeated expansion and contraction cycles.

Excessive convexity could result in overlap at the toes of the weld, which could create a stress riser or notch, this could, under the right circumstances, be a place for cracks to propogate.

[jazzalbart]

Well, I just want to recommend you that whatever laser medical instrument you use but be careful about its safety. Because Medical laser applications are based primarily on the properties of energy absorption and tissue interaction. So they can damage quickly.