C#数据每次运行只能将一个数据写入数据库

为什么我的数据库总是只能接收第一个数据而已，后面提供的数据都写不进数据库里面
private void timer1_Tick(object sender, EventArgs e)
{
if (this.Receive_TextBox.Text != "")
{ Insert(); }
}

SqlDataAdapter sda;
SqlDataAdapter sda1;
public void Insert()//将数据写入数据库
{
try
{ //截取字符串
string str = this.Receive_TextBox.Text.Trim().ToString();
string s = str.Substring(str.Length-8, 8);
SqlConnection conn = new SqlConnection(@"Server=PC-20161210PXBA\SQLEXPRESS;database=HM;uid=sa;pwd=");
conn.Open();

string str_sql = "insert into Sing(AttendanceDate,Attendancein,Attendanceout,ICcard) "
+ "values(@AttendanceDate,@Attendancein,@Attendanceout,@ICcard)";

SqlCommand cmd1 = new SqlCommand(str_sql, conn);

//SqlParameter parn2 = new SqlParameter("@EmployeeNo","");
//cmd1.Parameters.Add(parn2);
//SqlParameter parn1 = new SqlParameter("@EmployeeName","" );
//cmd1.Parameters.Add(parn1);
SqlParameter parn = new SqlParameter("@ICcard", s);
cmd1.Parameters.Add(parn);
SqlParameter parn3 = new SqlParameter("@AttendanceDate", dateTimeAttendDate.Value.ToString("yyyy-MM-dd ") + comboAttendIn.Text.Trim().ToString());
cmd1.Parameters.Add(parn3);
SqlParameter parn4 = new SqlParameter("@Attendancein", comboAttendIn.Text.Trim().ToString());
cmd1.Parameters.Add(parn4);
SqlParameter parn5 = new SqlParameter("@Attendanceout", comboAttendOut.Text.Trim().ToString());
cmd1.Parameters.Add(parn5);
// SqlParameter parn6 = new SqlParameter("@queqin", "");
//cmd1.Parameters.Add(parn6);


cmd1.ExecuteNonQuery();
conn.Close();
}
catch (Exception ex) { MessageBox.Show(ex.Message); }

}