Joining Copper Tubing 1

[Binary]

I'm new to a company that makes elbows out of copper tubing (1" through 6&quot. It is currently done by manual TIG welding.

Looking at the labour cost and the sketchy quality is making me wonder what is the state-of-the-art in such applications.

Is it TIG welding done by machine or is there some other joining technology that is suitable or ???

 

[CWIC]

Binary:
Cu is commonly (and readily) joined by GTAW. Before suggesting an alternative process that may not be feasible for you, I have a few questions regarding your current situation:

*Are your welders using turntables or other positioning equipment?
*What type of quality issues are you concerned with?
*What type of service are your elbows used for?

 

[MechEng13]

Binary,

One thing my company has looked at that sounds promising for this type of application is Friction welding. Basically the 2 parts are set in a machine similar to lathe, one part is spun to a set speed, then brought up against the other part, can be stationary or rotating at different speed. The force of the part spinning and being brought linearly against the other welds the 2 parts together. A salesman brought some samples and they had welded copper to steel, steel to steel, and others... The capital cost is kind of high, but once set up it's quick.


You may want to look into it.

Alan M. Etzkorn
Manufacturing Engineer
Hoffco/Comet Industries Inc.

http://www.hoffcocomet.com

 

[Binary]

CWIC:

*Are your welders using turntables or other positioning equipment?

The welders are using positioning fixtures to hold the copper tubing in place. When the weld brass flanges onto the copper, they do use turntables.

*What type of service are your elbows used for?

The elbows are used in RF transmission line. Therefore, they need to be gas-tight because they are filled with low-pressure inert gas while in service.

*What type of quality issues are you concerned with?

The primary quality issue is with reliably producing gas-tight assemblies. We currently do 100% inspection (cap line, pressureize, immerse in water, look for bubbles) which is very time consuming. We're currently seeing a rework rate on the order of 20%. What I'd like is to get to a point where we had the confidence to do away with the 100% immersion testing.

I've seen some elbows which appear to be soldered together or some similar type of process. They certainly did not have a GTAW bead.

 

[mcprofusion]

I concur with CWIC that you must carefully review the current process. Eliminate current manufacturing issues and identify your quality requirements. Bad welders don’t justify automation…....get them help!

If your still considering some type of automation, then your application needs to be looked at by a automation consultant, who will determine the level of automation practical for your application and perform a cost/profit cost analysis. GTAW (Tig) is a process that is automated regularly. Part quantity will generally be the determining factor in whether or not to automate.


MC PROFUSION
Toronto, Ontario, Canada
Website:

http://www.mcprofusion.com

 

[CWIC]

20%? Wow! That is quite a repair rate.

I am trying to help resolve your current process issues so you don't have to consider changing the present manufacturing process. Once again, without trying to keep you in suspense, I have a few more questions:

1.) Are the failures during the hydrostatic testing due to "gross" discontinuities? (e.g.: relatively large diameter porosity or areas of incomplete fusion)

2.) Are the parts visually inspected by qualified personnel prior to hydrostatic testing?

3.) Do the same weld discontinuities occur regardless of which welder is perfoming the work? (Are they consistent by all welding personnel?)

4.) Are you monitoring the frequency, type of repair, who performed the work, where the repairs occur on each part, etc., etc. and recording some statistical data to identify any trends?

FYI
Silver Soldering (not actually soldering) is another one of the most common methods of joining this material. It can also be just as problematic as the GTAW process. But, furnace soldering can be performed in bulk quantities. Like any other joining process, if part-preparation, consumables, process prarameters, etc. are not consistent, then simply changing manufacturing processes is not the answer for you.

mcprofusion noted: "Bad welders don’t justify automation…....get them help!" I agree.

 

[griffengm]

Would orbital welding systems apply here?
We've investigated them for our products but did not have the volume nor the joint configuration requirements to make it feasible for us but seems like they might be worth investigating here. If nothing else, it should reduce fatigue factors.

 

[Binary]

CWIC, I really appreciate your thoroughness.

1.) Are the failures during the hydrostatic testing due to "gross" discontinuities? (e.g.: relatively large diameter porosity or areas of incomplete fusion)

I'm not sure whether to call them "gross". They are not typically obvious to the untrained, naked eye (mine) but do generate a steady stream of small bubbles when submerged.

2.) Are the parts visually inspected by qualified personnel prior to hydrostatic testing?

The only inspection that takes place is by the welder who does the job. He self-inspects and then puts his completed parts on a rack. Judging by how much (little) we're paying the welders I suspect they may not be well-qualified to do the inspections (meaning they've not been trained or certified to AWS QC standards).

3.) Do the same weld discontinuities occur regardless of which welder is perfoming the work? (Are they consistent by all welding personnel?)

The lead guy in the shop was capable of consistently producing high-quality work that did not leak. He was the only one able to do so consistently. He was recently fired due to a personality conflict with his supervisor.

4.) Are you monitoring the frequency, type of repair, who performed the work, where the repairs occur on each part, etc., etc. and recording some statistical data to identify any trends?

Not currently. Is this typically done in production welding shops? I have no experience working around welding shops so I'm relying on the welders themselves to educate me.

My boss (an EE, not an ME), who also runs the shop floor, believes that this task should be done by silver soldering using induction heating equipment.

Silver Soldering... can also be just as problematic as the GTAW process.

That's my concern - I don't want to end up with simply exchanging one set of problems for another

Furnace soldering can be performed in bulk quantities.
What kinds of volumes justify this? Depending on the part, our maximum run size is probably fewer than 100 parts or so per month. We also have serious space constraints so furnaces are probably not a good option for us.

mcprofusion noted: "Bad welders don’t justify automation…....get them help!" I agree.
I agree, as well.

 

[CWIC]

Binary:
1.) "Gross" discontinuities would be obvious ones that the inspector/welders could easily observe. Minute pores such as those you describe would be hard to detect without visual aids.

*So you are encountering porosity. Fine posity is not uncommon whether you use silver soldering or GTAW to join the copper tubing. Cleaning of base materials is typically the source of this problem. I would review the material preparation process (including welding consumables) and the welding procedures (WPS's) that are being implemented. Excessive amperages sometimes result in the ERCuSi filler metal to boil out of the joint if these are sleeved connections. If these are butt joints, then the part cleanlines would be addressed to ensure a thorough cleaning has been performed prior to welding.

2.) You may want to consider informal or formal training for your welding personnel. Anyone who inspects a weld should be trained to do so. This is not an opnion but factual. I welded for years before I went to school and found out what the term discontinuity was. Then I had to learn where to apply the various terms, the cause or source of the discontinuities and the applicable corrective action. This is an acquired skill, it is not a process that can be performed without training and education.

*You may want to consider at least purchasing some visual inspection training materials such as the AWS B1.11:2000 Guide for the Visual Examination of Welds. One suggestion is that at least 1 member of your staff receive some formal training, then he/she can share this knowledge with others.
Ideally, if you could educate the entire staff involved with the production of these parts would be the way to go.

3.) If any one welder was performing acceptable workmanship, then there is a potential for all welders to do so.

*If one welder is capable of performing work that satisfies the accpetance criteria, then you should monitor the entire welding process and personnel to verify that all welders are performing the welding in the same manner using the same welding parameters (WPS).

4.) Monitoring and recording the source of any type of material or workmanship flaws is used in many industries. How else can you identify and resolve any quality-related issues?

*DOCUMENTATION: I recommend documenting the location of rejectable indications. e.g.: If all the pores are present at the start/stop areas of the welds, you may be encountering crater cracks which often have a small pore which extends through the part or weld bead thickness where the arc was terminated.
**EDUCATION: I would not rely on your welding personnel to educate you if they are creating these flaws and these same flaws are going undetected by the same personnel. For lack of a better analogy, this is like the blind leading the blind.
***PARTICIPATION: I would have the welders present at least a few times when the welds are being tested so they are part of the loop. They need to observe and be aware that the quality of their work is suffering.
****QUALIFICATION: Finally, I would require welders performing the work to qualify for this process. This is one way to confirm that the process can be performed by any one individual with satisfactory results.


The volume of work that justifies any manufacturing process (or a change) would be up to Binary.
*Is changing processes cost-effective for the product?
**Will you encounter more problems making the change to silver soldering vs. GTAW?


p.s.: My mistake regarding the testing you are performing, I don't know why I noted hydrotesting, you are specifically perfomimg bubble leak testing (BLT). My Level III would make me sit in the corner if he knew I noted that test method.

 

[griffengm]

The quantities you state are low for furnace brazing but the next question is how many lots. If you are running 10 lots of 100 in a month, it may be sufficient to look at another method.
Silver soldering does not necessarily need a furnace. It can be accomplished using an induction wand, flame, or resistance heating method. Any of these can be faster than tig if done correctly; most any can be slower if applied poorly. It sounds like most of your process is benchwork. This would make induction with some low level automation very doable for your products.
Silver solder however is more demanding in joint design regardless of the heating method than is tig. The productivity gains may just be worth the design time though.
Induction would remove turntables since the parts would be heated evenly on the entire circumference at one time. If a sheilding gas is necessary, that could also be done.
Just my 20 mils.
Griffy

 

[Beria]

Silver brazing copper is a good way to go----the pipe must be round----use an expander and a ring collar to expand into. Do not use induction heating---torch only. Use BCuP-5 alloy-----------only use an experienced silver brazer. If no experienced brazer available--mechanize the system. Abrade male component O.D. and clean with a good solvent. Slow and even is a good practice for heating.