ElgiEquipments production increased more than four times on using Studer’s turning and grinding machine | By Indira Rao | Coimbatore based Elgi Equipments is a leading air compressor manufacturer with a broad line of innovative and technologically superior compressed air systems. It is one of the few companies in the world capable of designing, manufacturing air ends and compressor packages.
“We manufacture reciprocating air compressors, rotary screw air compressors, oil-flooded, oil-free and centrifugal air compressors and precision engineered components. Screw compression elements are manufactured in-house using state-ofthe- art machining centres for rotor grinding and machining intrinsic castings of various sizes. Our own eta-V profile rotors deliver more compressed air while consuming less energy,” stated SubashRamdoss, corporate, manufacturing engineering, ElgiEquipments.
The company’s manufacturing facilities are equipped with advanced, high precision rotor grinding machines, turning centres, CNC horizontal and CNC vertical machining centres. The in-house rotor manufacturing facility provides them with unrivalled advantage over competition.
“In our machining process for the rotors, we have to maintain very tight tolerances on the journal diameters, OD of the screw and gear seating diameters. This was a challenge since we had to do the same through multiple setups on individual turning and grinding machines,” averred Ramdoss.
The machining process involved turning the shafts of left and right side to required diameters in two separate setups. The grinding of the shafts was next done in two individual setups on cylindrical grinding machines and the screw OD was done in yet another individual setup. Complete shaft machining alone involved five setups. The setup time totally was four hours and the machining time per rotor was around 40 minutes.
“Every day close to 40 unique types of rotors need to be produced for the assembly line with a batch quantity varying from maximum of 10 to as low as one. This long sequence of process, coupled with the high variety – low volume batch sizes, resulted in long lead times and higher amount of WIP in the machining loop. The machining team had to be on their toes to ensure and maintain the quality during the entire machining process, setup change, material handling and transportation between processes,” said Ramdoss.
While they were evaluating alternate manufacturing processes to simplify and stream line the rotor manufacturing process Elgi came across Studer. “We were in discussion with Elgi for a long time for various projects, and then in 2011 we showed them a video of machining that was done on a compressor shaft in a single clamping followed by presentation of the S242 machine and the benefits of the same.
That caught their interest as they were also looking out for a better solution for their compressor screw machining,” mentioned Sreekanteswar S, president, United Grinding. Studer proposed the S242 grinding cum turning machine to manufacture Elgi’s rotors. The manufacturing sequence on the machine promised to bring down the setups from five to one and the machining time was expected to be down by 50%. A process capability of CpK>1.67 was also promised.
The team was confident of achieving these results on the machine under normal shop floor temperatures without the need to have controlled environment for the machine. “This made the proposal very interesting for us and hence we went into discussion on planning the manufacturing process for trials at Studer’s facility. We had initial doubts on how stable the process would be since we would be removing a lot of material in the turning process and then immediately following it up with a very precision grinding process,” quipped Ramdoss.
The process did not hit the bull’s eye right from the start. They were some rough spots, which were taken care of immediately. Seconding Ramdoss added, “The entire CpK trial process itself involved the machine cycle for a period of close to 20 hrs. In our first few runs we had some problems in meeting the process capability for some dimensions.”
Studer again worked with them to revisit and fine tune some of the parameters in the process. “With some modifications in the holding and gauging process we ran the second set of trial successfully. All our targets related to quality and productivity were met for all the models we planned to manufacture on the machine,” said Ramdoss.
The rotor shaft is a heart of the air compressor as it rotates at high RPM and produces the positive air pressure. Rotor shaft OD, side faces and bearing diameters are to be maintained in tight geometrical tolerances which directly affects the performance of the compressor. The S242 combination turning and grinding solution provided by Studer ideally combines the technologies of cylindrical grinding, hard turning and key way milling. Thanks to its stable and sturdy design concept, it can easily cope with the three different processes like at Elgi.
“Consequently, it enables highly efficient fine machining of shafts and chucking components with a high manufacturing quality and production reliability and is therefore the cost-optimal manufacturing method for machining high-precision hardened work pieces. Short changeover times are a further strength of the S242.
This makes it attractive for both large-scale production and for small batch sizes and single parts,” explained Sreekanteswar. The project at Elgi was a multi-tasking one which included combined operations turning, grinding and milling. The machine had to be tuned to carry out the two opposite processes – one of high material removal with coarse accuracies and the other of contrastingly low material removal with very high accuracy and surface finish.
“Further the range of parts covered in the project were many from big to small, heavy to light weight, etc. This poses challenges in terms of providing suitable fixtures for clamping the wide variety of parts. Minute care had to be taken of even elementary processes like chip disposal, as the machine generated long and twisty turning chips and also fine grinding dust, both of which had to be evacuated using a single chip conveyor system,” stated Sreekanteswar. This precision led to several benefits at Elgi. Elucidating on the same, Ramdoss ascertained, “We achieved a reduction in setup and process time by 50%. The throughput time for a rotor also came down by 25%.”
“The WIP inventory for the rotors was brought down by 40% in the shop floor. Our queues of rotors waiting for grinding and turning process almost disappeared. Most importantly the quality of the rotor was now assured since it was all being manufactured and controlled in one setup!” Moving forward, Elgi is now in discussion with the Studer team to fine tune their manufacturing process towards optimising process parameters to further reduce their cycle and setup time.