Fasteners and Welding Lecture 22 Autumn Quarter

What’s Coming Up? Today Fasteners & Welding Tuesday Working Drawing Set Wednesday Measurements Lab Thursday Quiz on Fasteners and Welding Introduction to AutoDesk Inventor Instructor: Fasteners and Welding are the last items needed before studying working drawings. Working drawings have an assembly, parts list, and details of each part. The assembly shows how the parts fit together and the information on fasteners and welding is needed. Autumn Quarter

Fasteners and Welding Objectives: Understand importance of fasteners, learn how to specify threaded fasteners and represent them in drawings and learn about other fastening methods. Understand basics of welding symbols Instructor: We find fasteners of all kinds in daily life – buttons, zippers, velcro, wood screws, nuts and bolts, clips, etc. In this session we are going to deal primarily with threaded fasteners. We will follow fasteners with the discussion of weldng symbols. Autumn Quarter

Topics For Today Importance of fastening Threaded fasteners Non-threaded fasteners Other machine elements Adhesives Welding Instructor: There are non threaded fasteners such as clips and rivets. We will talk only briefly about adhesives but they play a large role in assemblies. Autumn Quarter

Importance of Fastening 50% of production time for the average item is spent on assembly/fastening. Fasteners are critical to product performance and reliability Choosing the proper fasteners is an important part of product design Instructor: The first bullet talks about how manufacturing time is spent on fasteners and assembly. Toyota saved time and money a few years ago when the changed the rear bumper sub assembly from 7 parts to 3 parts. Autumn Quarter

Three Methods Commonly Used in Fastening Mechanical Fastening Bolts, screws, rivets, keys, pins Paper clips, zippers, “Velcro” Bonding Welding, soldering, brazing, gluing Forming Sheet metal, plastic snaps parts Instructor: This slide shows one way to categorize fastening. Autumn Quarter

Threaded Fasteners – Terminology Instructor: If possible, find some large nuts and bolts or any nuts and bolts to pass around the class when you start this discussion of threaded fasteners. Remind the students that this knowledge about threaded fasteners will help them when they have to go the hardware store for parts. External Threads Autumn Quarter

Threaded Fasteners – Terminology Internal threads Threads inside a hole Made by drill & tap: drill smooth hole make threads with a tap Instructor: If possible, purchase a tap or borrow one from the machine shop to pass around. Oil is used many times to help cutting the threads and keep the tap cool. Autumn Quarter

Threaded Fasteners – Terminology Bolt - head on one end, threads on other end, used with a nut Stud - rod threaded at both ends Cap screw - head on one end, threads on other end, NOT used with a nut Machine screw - similar to cap screw but smaller Set screw - used to prevent 2 rotating parts from moving separately Instructor: Again, it is a good idea to have real examples of these parts to pass around. It is even better if you can find an assembly that has these fasteners included. Autumn Quarter

Threaded Fasteners – Specification Example of a typical thread specification (in inches) .5 - 28 UNC - 3 B .5 - major diameter of .5 inches 28 - 28 threads per inch UN - form Unified (i.e. shape of the thread)* C - series (C means coarse), F (fine), EF (extra fine) Instructor: In the hardware store, they probably have boxes that just say ½ - 28 and the length of the bolt. * There are several thread forms. UN is common. Autumn Quarter

Threaded Fasteners – Specification Continuation of example of a typical thread specification (in inches) .5 - 28 UNC - 3 B 3 - class of fit (3 is precise, 2 is normal, 1 is loose fit) B - internal thread (A is for external) Instructor: Let the students know that they will have to know this information to solve the working drawing problem that is coming later this week. This material will also be on the midterm exam or the final exam. Autumn Quarter

Threaded Fasteners – Specification Example of a typical metric thread specification M6 x 1 - 4H5H M - indicates thread form is metric 6 - major diameter in millimeters 1 - pitch in millimeters 4H5H - tolerance (capital letters for internal thread, lower case for external thread) Instructor: This is an example of a metric thead note. Today, in the US many car parts are metric rather than inch. Note that the metric thread notes start with M. Note also that in the inch based thread note, the number of threads per inch is given while in the metric threads it is the pitch or distance between threads. Number of threads per inch = 1/pitch. The tolerance shown here is the equivalent of the class of fit in the inch-based notes. Autumn Quarter

Representing External Threads Options for representing external threads in a drawing Schematic 2. 1. End View Detailed Instructor: The detailed threads took so long to draw by hand that the schematic and simplified representations were developed. However, with CAD systems it does not take long to create the detailed thread symbols once and use them over and over. Note in the schematic representation that the thin lines represent the crests of the threads and the shorter, thicker lines represent the root. Where possible the spacing between the thin lines should be the pitch on the actual thread. For small fasteners with fine threads this convention is relaxed. Autumn Quarter

Representing Internal Threads Options for representing internal threads Schematic (in section) Detailed (in section) Unsectioned End View Instructor: Note that in the end view of the drilled and tapped hole the visible circle is the diameter of the drill bit that was used to create (drill) the hole and the hidden circle represents the diameter of the cutting edges of the tap. Autumn Quarter

Non-Threaded Fasteners Rivets Pins Keys Retaining rings Locking washers Instructor: Again, bring in rivets, pins, keys, retaining rings and washers of various kinds. If you cannot find the actual fasteners, show pictures from the book or from catalogs. Tell the students that there are Appendices that have tables for all kinds of fasteners. An example of a retaining ring is the clip that is used to hold on a door handle or window crank in a car. Lock washers can be found on the bicycle axles to keep the nuts from loosening. If there are fenders on the bicycle they are probably fastened by rivets. Autumn Quarter

Other Machine Elements Springs Bushings Bearings (See references for more details) Instructor: Here are more items that you should bring for the class to see. The springs were discussed in one of the labs earlier in the term. Bushings are typically softer metal (bronze) used to protect the harder parts (steel or cast iron). They are typically force fit into the hole and have a clearance fit with the shaft. Bearings are usually ball or roller bearings where the balls or rollers are held in place by inner and outer retaining rings. Autumn Quarter

Adhesives Used to join thin or dissimilar materials Seal a joint as well as bond it Can be used to coat threads and prevent loosening Instructor: It is difficult to find guidelines as to how to write specifications for adhesives. If your students are going to build robots, the third bullet is important if they are using nuts and bolts to do the assembly. They should purchase something like Loctite™ for this purpose or they can use cheap fingernail polish. Autumn Quarter

Thermal Fastening Soldering - solder (filler) melts but parts to be joined remain at low temperature Brazing - filler is melted, and parts to be joined are heated but do not melt. Can be used to join dissimilar metals Welding - parts to be joined and filler (if any) are melted, pressed together and then cool. (See Section 9.8 in BTG) Instructor: Soldering and brazing use metal alloys that melt at lower temperatures than the parts that they are joining. When welding the filler metal is the same as the parts that are being joined and the filler and portions of the parts to be joined all melt. In these three processes, the temperature and the strength of the bond both increase from soldering to welding. Autumn Quarter

Welding Symbol Reference Line Leader and arrow Basic weld symbol (location & depth of weld) Finish symbol Weld symbol Dimensions Supplementary symbols Tail and specifications Instructor: Welding symbols can quickly become complicated. Have the students look at the examples in the text and in the appendix that deals with weld symbols. Autumn Quarter

Welding Symbol Leader Reference Line Tail Autumn Quarter

Welding Symbol – Example Fillet Weld Weld around Arrow side Opposite side Instructor: There are many different types of welds and associated weld symbols. Again refer them to the Appendix to see all of the possibilities. Specification Result Autumn Quarter

Welding Symbol Below reference line describes the ARROW side of the weld Above the line describes the OTHER side Joint described by symbol (fillet, square) Numbers by symbol indicate size Circle at joint specifies weld around Autumn Quarter

References Threaded and Other Fasteners BTG Chapter 9, Appendices A24 – A42 Welding BTG Appendix B.25 Autumn Quarter

Assignments Dwg 43 – FB-1D – Fasteners Answer questions about fasteners using the tables in the book. Due Today Dwg 44 – FD-3B – Welding Symbology Add notes to the Welding Symbols as needed to make them match the schematic Due Tuesday Dwg 45 – Working Drawing Set A Handout will be provided in class Instructor: The students will do only one page on fasteners and one page on welding before they start to work on the working drawing set. The working drawing set should give them more experience in this area. Most CAD packages have dimensioning and note capabilities so that thread notes and weld symbols can be added to drawings. Autumn Quarter