Spindle Capabilities & Capacity
Colonial Tool's spindle product line carries the trademark of “R.A.S. – Rigidity At Speed” and was permitted to continue using the Ex—Cell-O name until 1992. Recently R.A.S. was awarded a patent on our state of the art R.A.S. Motorized Boring Spindle.
R.A.S. has produced over 150,000 spindles in the past 70 years which includes block, motorized, eccentric, aerostatic and hydrostaﬁc spindles.
R.A.S. – Colonial Tool is a complete self—contained engineering, manufacturing, assembly and service facility which is capable providing precision spindle requirements at the highest quality level and lowest cost.
R.A.S. engineering reviews the customer requirements and will select the spindle designs for optimum performance. R.A.S. is CAD/CAE integrated using the most efficient and accurate software for spindle analysis. R.A.S. also employs engineering consulting firms when overflow dictates the necessity. These firms include Adesco, Demac and Engineering Methods.
l. Metal Cutting
R.A.S. Colonial Tool is a completely self-sufficient manufacturing facility that ideally requires no subcontracting other than raw materials and bearings. This is especially significant during critical deliveries (1'.e., warranty repairs) when turnaround is important.
Virtually any shaft or housing configuration can be manufactured at our facility and currently 95% of the shafts and 80% of the housings are manufactured at Colonial Tool.
R.A.S. Colonial Tool has a 10,000 square foot heat treatment facility and that can select and control the heat treat processes to ensure material stability.
C. Assemble and Service
R.A.S. has a 1700 square foot clean room, temperature and humidity controlled where all assembly of the spindles is completed and tested. The R.A.S. spindle technicians are capable of assembly and test of 60-70 standard box spindles or 35-45 standard motorized spindles (i.e., $ 550K U.S./month). When excess capacity is required, Colonial Tool has assigned project engineers to subcontract assembly facilities to coordinate the assemblies. The local subcontract assembly facility untilized by R.A.S. is Precision Spindle Services and G & H Machine who have 30 years experience in spindle assembly and a long relationship with R.A.S. The capacity can then be expanded to S 750K U.S./month.
A 24 hour service hot—line is availiable to all customers. All servicing will be completed out of Colonial Tool—Windsor and R.A.S. assures a representative at the customer facility within one hour of telephone communication.
D. Project Management
All programs will require full commitment of R.A.S. - Colonial Tool to provide the necessary product and service expected in a partnership. Project Management will be the responsibility of the Vice President of Operations - Paul Thrasher, P. Eng. who has l0 years of experience in the automotive industry.
The program responsibilities of any spindle order are divided among the personnel at Colonial Tool.
R.A.S. standard delivery times are dependent upon the style of spindle and the quantity. Commonality between spindles greatly increases the efficiency of the spindles and should be striven for in projects of any magnitude.
Generally, quoted deliveries are based upon receipt of first approval drawings.
Spindle quantities greater than indicated are usually on a release basis
NUMBER OF WEEKS 8 10 12 14 16 18
BOX SPINDLES 16 24 32
MOTORIZED SPINDLES - - - 8 16 24
SPECIALS - - - - 8 16
(CLUSTER/ GEAR DRIVEN)
SPINDLE RANGE FEATURES
R.A.S. standard box spindle range has many features that make it an excellent choice for critical manufacturing operations. Within this section are the features that Ford has enquired about as well as characteristics that R.A.S. believes should be highlighted.
Deviations from the axis of rotation occur when static and dynamic forces are applied to the spindle. It is the resistance of these forces which we define as the static stiffness and dynamic stiffness.
A. Static Stiffness
Precision machining, generally finishing operations, require statically rigid spindles to ensure cutting accuracy. Resultant radial spindle spring rates are comprised of two main components; shaft bending and bearing deflection. See Figure.
Studying the bearing contribution, the deflections are a function of bearing stiffness, overhang from front bearing to cutting force and span between bearings.
KBRC = F/dBR ...(1)
dBRC = (a * dBRC + (dB * 1/dA + dB) * d2+d2/dB+1 ...(2)
dB = F(a + 1)/1*XB ...(3)
dA = F(a + 1)/1*XA ...(4)
The contribution of shaft bending is dependent on shaft material and geometry, overhang from front bearings to cutting face and span betwec,.; bearings.
KBRC = F/dGEO„ ...(5)
dGEO = …. (6)
E = Modulus of elasticity
I = 3.1416172/64 Assuming constant moment of inertia
The combined stiffness of the bearing and shaft is inversely proportional to sum of the deflections.
Therefore KSTATIC = …. (7)
The equations shown above are a simplified version of the radial static spring rates of spindle bearing assemblies. In practice, deflections are frequently greater than the calculated values because of the integrity of bearing fits, deformation of mating surfaces, and the effects of housing construction. The integrity of bearing fits can be improved by increased preload which expands the outer ring of the bearing for a more intimate fit. The most important use of the equations shown is to ascertain bearing design, span between bearings; shaft geometry and sometimes materials selected, which will provide the least deviation of the spindle axis.
Spindles are also subject to axial deflection, which the spindle must be designed to overcome. For simplicity purposes, the spindle axial spring rates can be assumed equal to the bearing spring rates. Therefore, the spindle assembly is a function of bearing type, preload and configuration
B. DYNAMIC STIFFNESS
Susceptibility to chatter is directly related to dynamic flexibility. The dependents of dynamic flexibility are combined within the tool-workplace circuit, at which point the spindle bearing assembly is a math factor.
To simplify the explanation of dynamic stiffness, a simple dampened spring-mass system is considered, represented in equation 8.
As the frequency of the forced vibration is increased, the amplitude of the vibration is increased. When the forced vibration frequency (W) equals the natural frequency (Wn) of the spring mass system resonance occurs KDTN = KSTAT * 20). Dynamic flexibility is the amplitude of vibration at resonance and dependant only on the amount of dampening (z) in the system. Minimizing the vibration amplitude requires increased dampening which emanates from hysteresis of the spindle material and bearing friction. The dampening properties of rolling elements are not sufficiently known, which makes spindle dynamic behaviour difficult to predict, however, tests have indicated that dampening is more effective as preload is increased.
C. WARD SPINDLES STIFFNESSES
Static stiffness values have been generated for the R.A.S. standard spindle range. These stiffnesses are calculated based on many assumptions and are consistent through the tabulation. See Table 7. Note comparison of calculated stiffness from different spindle builders is not advised without the degree of assumption influences emphasized.
D. SUGGESTED STIFFNESS
R.A.S. has established some target values for spindle spring rates at the spindle nose which have proven superior for the tooling utilized.
SPINDLE SPECIAL NOSES
R.A.S. spindle units are universally applicable and are supplied with various nose configurations, depending on the requirements. Figures 6 through 8 illustrate the nose configurations available.
TOOL JOINT INTERFACE
The R.A.S. spindle tool joint interface is heat treated, and usually to 58-62 R'c'. High hardness at the interface results in a wear resistant surface which does not require any additional treatments.
Black oxiding and chroming of the spindle face are unacceptable because of the induce variability and the flaking of chrome, however, chroming pilot diameters can be successfully accomplished without fear of peeling or chipping. Chroming is used frequently during the rebuilding of spindles to bring the pilot diameters into tolerance.
R.A.S. employs A.C. induction motors, the standard motorized precision spindles having special characteristics for longer life and better performance.
a. Bore of the rotor is honed for best possible cylindricity reducing stress when the motor is shrunk fit on the shaft.
b. Outside diameter of the rotor is finish ground concentric to the bearing diameters reducing balance problems ( reduce torque pulse ).
c. Motors requiring liquid cooling have stainless steel shells to prevent corrosion of the shell.
d. Stators are electrically balanced limiting uneven loading of the rotors.
e. Windings include vacuum impregnated insulation and Nomex coating to ensure maximum protection from contaminants.
R.A.S. utilizes a tube spacer in the design of the standard spindles up to 100 mm shaft diameters. The advantages of using a tube spacer is two-fold. First, the spacer allows for the use of the same diameter bearings in the front and rear of the spindle reducing the number of different components. The second is the advantage of increased stiffness. Primarily the limiting factor in spindle stiffness under 100 mm is attributed to the shaft geometry. The tube spacer adds greater stability and rigidity due to clamping the bearings between the spacer. If we imagine a thin section of shaft with similar discs attached to each end we can realize some flexibility between the discs. However, if a tube spacer is put over the shaft and clamped tightly between the discs, the stiffness of the system will increase.
R.A.S. utilizes several high quality standard materials in all the standard spindle ranges. Outlined within are the materials, properties and typical uses (Table 8 and 9). Depending on the application, other exotic materials may be required, such as Teconite 18.5, where a high modulus of elasticity is required to increase rigidity.
R.A.S. manufactures all standard spindles to the ISO precision tolerances or better outlined. in Tables 9 to 10 and Appendix I. Figures 8 and 9 are standard components used on DBLM-075-000 spindle which indicates the precision and quality employed in the box spindles. Where exceptional precision is required, the tolerances illustrated are reduced and special manufacturing techniques are used to achieve them. (i.e. Aero Static Spindles)