plasma newbie question

[georgebarr]

I just discovered a tool workshop rental place 30 minutes from my house at http://techshop.ws. This means I will have access to a CNC Plasma machine. I have a question. Can CNC Plasma produce shapes from 3/8" mild steel plates without increasing the thickness of the plate? Some methods do increase the thickness slightly along the area where material was removed. Also, will the cuts be squared and not slightly angled like you get with water jet? Is there a way to control these 2 undesirable things?

Thanks,

[jimcolt]

I have never heard of plasma increasing the thickness of the plate edge. Edge squareness with the plasma system can be relatively square...or can be quite tapered depending on the Plasma system (there are low end air plasma systems that cost $500, and there are high performance oxygen plasma systems that cost $45,000...the cut quality, tolerance and metalurgical side effects are better with the high end industrial systems!), the cnc machine's motion capability in terms of cut path accuracy and acceleration rates, the torch height control systems ability to pierce and cut at the proper heights, and the part program.

Edge squareness can be less than 1 degree on many materials using the right plasma cutting equipment.

The sample in the picture is 3/8" carbon steel cut with a Hypertherm HPR130 high performance plasma with oxygen as the plasma gas and air as the shield....it is cut at 80 Amps at 75 inches per minute. The hole (that is tapped) was 5/16 diameter...and was tapped with a standard ($3.00) Craftsmen brand tap to demonstrate that there is minimal hardening of the edge with this process. You could not tap the hole if the part was cut with an air plasma!

Jim Colt

[georgebarr]

jimcolt,

What is the cheapest price Oxygen Plasma machine? How about an Air Plasma costing aroung $1500. I am trying to balance cost with performance here. I will need to make holes that can be tapped without any problems on 3/8" mild steel plates.

Thanks,

[jimcolt]

The less expensive oxygen plasma systems (from Hypertherm, the Max 200 and the HSD130....around $12,500 and $16,000 respectively) are not High Definition quality...and I would not expect them to be able to produce adequate quality on small holes that would allow for tapping. Conventional plasma's will produce more edge taper....which can be more pronounced as the holes get smaller in diameter.

A high definition quality plasma (such as the Hypertherm HPR130, around $31,000) produces higher energy density at the arc....and, when coupled to a precision cutting machine and THC...can produce very nice holes with minimal taper.

Jim Colt

[jeffery71]

This is might be a dumb question and I think I may know the answer. But why do High def plasma cutters cost so much? I mean is there really alot to them? or is it more like Hypertherms THC units way over priced but there is a small market so need to charge more. Don't take that the wrong way. I am all for charging as much as you can for a product. I just think 30 thousand for a plasma seems like alot. Lets see a nice car costs about 30 thousand. The last part I made for a customer cost them 45 bucks and they seamed pissed cause I charged that much. I acutally didn't even charge them for all my time in it. Go figure.


Jeff

[jimcolt]

Jeff,

A really good question....I will give you my best answer.

1st......yes pricing in a small way has something to do with manufacturing volume. As an example....we sell more than 50,000 Powermax type systems per year...and roughly 6000 HPR type systems in the same time period. You used a car analogy....a nice 4 door sedan is 30,000....way more complex than the plasma system....yet it is produced generally in production numbers that approach 250,000 units per year. If you look at a specialty car that is made in quantities of less than 10,000 units annually....you will see a price that can easily be 5 to 10 times the high production vehicle......and it probably is not as reliable! (Maserati, Rolls Royce, Ferrari, etc.)

Of more effect to the price however is the compexity and the design and the sheer robustness required in a Plasma that must operate 24 hours a day, 365 days a year in a dirty industrial environment.

A Powermax air plasma (relatively low cost) is one box that houses a (very high tech) inverter based DC power supply....an air regulator/solenoid, and a microprocessor board that controls the out put current....does special ramp up and ramp down of output power to enhance consumable life....and controls on and off times of the pilot arc current for reliable starting. Powermax systems are designed to be lightweight, portable and cost competitive with other manufacturers plasma systems....and do not have 100% duty cycle at full output power. A 100 Amp Powermax 1650 with a 25' machine torch retails for $5460. It can cut with air or nitrogen.

An HPR130 is comprised of the (main big box) a chopper based DC power supply, a pilot arc controller circuit, a liquid coolant recirculating system, a microprocessor based control circuit with can bus and serial communication ability.There also is a remotely mounted (near where the operator of the cutting machine works) gas flow control panel that uses pulse width modulated valves and real time pressure feedback loops to monitor and adjust preflow, ramp up, cutflow and ramp down gas pressures in coordination with the particular process being used (for cutting different materials and different thicknesses at power levels between 30 and 130 Amps)...this gas control is available in a fully automatic version that is controlled by data from the cnc control....or in a manual version that the operator sets.There is also a gas mixing panel that is mounted within 72 inches of the torch, this panel does critical ramp up and ramp down gas pressure changes that need to be done in close proximity to the torch....these adjustments are critical to consumable life...it is not uncommon to get 2 miles and thousands of starts out of one set of consumables on this type of system! There is also another box called the remote ignition console...this is normally mounted near the torch and houses a solid state, high frequency, high voltage discharge to ignite the torch reliably. Of course there are interconnecting cables that carry power and canBus serial data to each one of these boxes to coordinate everything. HPR130, $31,000.

The Powermax can use air or nitrogen. The torch is not liquid cooled. Consumables are less complex and less expensive...yet they do not last as long due to simple gas control, lack of liquid cooling and a less sophisticated process to keep things simple and portable.

The HPR can use air, oxygen, nitrogen argon/hydrogen, nitrogen/hydrogen as the plasma gas and air, oxygen, nitrogen as the shield gas to fine tune the process metalurgically to the customers desires. The HPR is 100% duty cycle at its maximum output under high ambient temperature conditions. The consumables cost more, yet last far longer that the Powermax units...resulting in lower cost per foot of cut, with superior cut quality.

I can continue with comparisons. Inreality there is a need for both types of product....and the costs can be justified with the performance. I invite anyone interested for a tour of our facility in New Hampshire to see our engineering, research, reliability labs and production processes....just contact me for a tour!

Best regards, Jim Colt

[jeffery71]

Jim,

Thanks, A very informative post. "2 miles and thousands of starts out of one set of consumables" I bet the consumables cost a pretty penny! But if compared to how long they last probably not. I wish I could take you up on your offer to visit you in New Hampshire. Unfortunately I can't, but that would be just the type of trip I would love. Forget Disney World. I get more fun out of visiting manufacturing plants!

Jeff

[xjdubber]

Really the coolest thing I find about the HPR series is the autogas console, automatically picking gasses and mixing them right for the material being cut. that is pimp!