Research On Closed-Loop Control Of Laser Engineered Net Shaping Of The Unequal-Height Parts

Unequal height structural parts with a large amount of complex structure including overhang,circular sector,and bend exist in the industrial production.The adoption of traditional processing technology,such as casting and plastic working,can only used for relatively simple structure with mass production,when facing too complex structure,high precision,and too concentrated demand,traditional processing technology is difficult to achieve that.Laser engineered net shaping technology is greatly made up for the defects,by laser scanning and metal deposition,without use of mould,accumulated fine structural parts can meet the requirements by series layer scanning.After that,only a small amount of machining or no longer needed to meet the technological requirements,and put into the production application.On the basis of this process,this paper studied the closed-loop control of the laser engineered net shaping in unequal height structural parts by using the layer height acquisition device and combining with cladding sprayer with inside-beam powder feeding.Taking KUKA six-axis robot as sports media,equipped with laser,powder feeder and nitrogen-making device,a set of closed-loop control system in laser engineered net shaping was built with laser inside-beam powder feeding coaxial powder feeding cladding sprayer as the core technology and combining with the height measuring device,to study the closed-loop forming in unequal height structural parts.Based on the method of normal hierarchical path planning and floor height measurement system,a new method of layering and sectioning fusion covering closed-loop control is proposed.Section and bend thin-walled parts are normal layered,and divided into several unequal height melting channel.Each melting channel is divide equally into several segments along the scanning direction.Added tiny transition section is used to adjust the position of the sprayer and pose of each starting position.Based on high speed CCD camera as the floor height measuring system designed by visual sensor,it real-time feedback the actual stacker of each section in every layer,performing timely correction for lifting capacity of KUKA robot in Z-axis,to ensure that defocusing amount of each section in the next layer will not change,and make ensure that the width of the forming parts is consistent.Speed PI controller was designed,through the feedback of error of each section in each layer between the actual stacker and expected stacker,to adjust the scanning speed of each section in next layer,which will make actual stacker of each layer be able to level off to its expected stacker.At the same time,gradually making up for previous accumulated stacker error of each section,to guarantee the actual total stacker and the expected total stacker of each section is consistent,and ensure the size accuracy of forming parts.Moreover,the effect of high precision eventually leads to the forming of circular sector and bend thin-walled structural parts in fine smooth appearance and excellent size.It is proved that the speed PI controller has obvious regulating effect by the analysis of actual stacker oscillogram of each section of formed parts: the appearance is smooth,without obvious bulge and collapse,and the size error is very small;Implementing microstructure analysis of the forming parts: the grain size grade is basically the same everywhere,and it is the dendrite that grows along a certain direction.Through the above experimental verification,it is proved that,based on the floor height measuring system,designed speed PI controller by this paper holds obvious effect over laser near-net closed-loop shaping of unequal height structural parts,which greatly improves the success rate of the forming of complex structure and significantly increases forming accuracy.