Steve Zlotnicki Click image to enlargeby Steve Zlotnick

How to achieve consistent cutting results

Oxy-fuel torch cutting, or flame cutting, is by far the oldest cutting process for mild steel. It is generally viewed as a simple process, and the equipment and consumables are relatively inexpensive. An oxy-fuel torch can cut through very thick plate, limited primarily by the amount of oxygen that can be delivered. When adjusted properly, an oxy-fuel torch delivers a smooth, square cut surface. There is little slag on the bottom edge and the top edge is only slightly rounded from preheat flames. This surface is ideally suited for many applications without further treatment. Consistently achieving good cut quality with oxy-fuel requires understanding the factors that impact cutting results. While there are a number of factors to consider, the following are the root of most common cut quality issues.

Cutting Speed Too Low
An abnormally low cutting speed results in heavy gouging of the cut surface and slag adhering in large globules. Under this condition, oxygen and fuel gas are being wasted.

Cutting Speed Too High
An extremely high cutting speed results in heavy lag, indicated by the curved lag lines on the cut surface. The face is reasonably smooth but somewhat concave. Slag will adhere during cutting, but it may be removed with ease. Heavy lag cutting is recommended for straight line cuts only.

Nozzle Too Far From Surface
When the nozzle is too high above the work, excessive rounding of the top edge occurs. The cutting speed may have to be lowered. With the correct nozzle clearance, preheat flames should not be more than 1/4 in. (6.35 mm) above the top surface of the plate.

Nozzle Too Near Surface
When the nozzle is too low, part of the preheat flame's inner cones become buried in the cutting kerf. This produces grooves in the cut face and excessive melting of the top edge. In addition, the flame becomes subject to popping and lost cuts may result.

Excess Cutting Oxygen
If the cutting oxygen pressure is too high or the nozzle size too large, a reduction in cut quality will result. Nozzles are made to operate within a limited range of torch pressures. Therefore, excessive oxygen pressure causes distortions in the oxygen stream once it leaves the nozzle.

Excess Preheat Flame
Inexperienced operators often try to increase cutting speeds by using a heavy preheat flame. Excessive preheat causes melting of the top edge and may actually lower the speed of cutting. Moreover, oxygen and fuel gas are wasted.

Dirty Nozzle
If the nozzle has been fouled, it may cause the oxygen stream to lose its parallel form. The cut surface will not be smooth and square, and there may be pitting, under-cutting, heavy slag or scale. The nozzle should be cleaned with care, so as not to distort, or bell-mouth, the cutting oxygen bore.

Being aware of the factors that can influence oxy-fuel cut quality and making the proper allowances for them can help machine operators consistently achieve high quality cutting results that rivals that of a machined surface. SMT

Steve Zlotnicki is product manager, cutting, with ESAB Welding & Cutting Products, Florence, SC .

 

Simulating Five

No matter how easy to operate, few would argue that five axis machining centres are more prone to tool and fixture interference than those limited to three axis work.

Mazak runs CNC program challenge

Two machines side-by-side. Same part. Same program. Very different results.

Form Tapping Advances

by Sam Matsumoto 

Recent advances have overcome past limitations

Fabricating while sleeping

Lights out automation means Alberta fabricator doesn’t have to turn business away

by Patty Jessome

The problem Increasing production and flexibility 

The solution Investing in automated lights out punch/laser technology

Pumping Up Productivity

by Noelle Stapinsky

Advancements in waterjet pump technologies are improving pressure delivery 

Revisiting Free Trade

US President Donald Trump says he wants to make America great again and part of his plan is to rip up free trade agreements and bring manufacturing back into the US.

Staying Sharp

by Mary Scianna

Blade failure can have a catastrophic impact on your sawing operations

Bystronic Canada appoints new direct sales engineer

Bystronic Canada has appointed David Golls as direct sales engineer for Alberta and British Columbia.

Electric panel bender bends in less than 2 seconds

Salvagnini's P1 100 per cent electric panel bender is desgined to bend panels with just 3 kW and is equipped with patented bending kinematics. The machine can make bends in less than two seconds. The bender is a good solution for companies working with cell production. 

FABTECH 2014: Harnessing software for smarter fabricating

While new and innovative machines were in abundance at FABTECH 2014, what dominated the show floor was software and how suppliers are harnessing the power of software technology to create smarter fabricating solutions.

Spindle, toolholder hygiene checklist

by Nicholas J. Korfias

8 tips to maintain toolholder-machine spindle interface accuracy

Ontario auto parts manufacturers to receive $1.4 M in funding

Twenty Ontario automotive parts manufacturing will be receiving $1.4 million in funding from the Automotive Supplier Competitiveness Improvement Program (ASCIP).

MC Machinery showcases manufacturing technology

MC Machinery opened its doors to customers on June 4 to showcase its wide range of machining and fabricating technologies, including a metal laser sintering hybrid milling machine and fiber laser cutting technology.

Stay In Touch

twitter facebook linkedIn